From 75f56cd3e1c310cccee5c0755003a6b3ecd7f50f Mon Sep 17 00:00:00 2001
From: Paul Davis <paul@linuxaudiosystems.com>
Date: Wed, 25 Sep 2024 18:38:49 -0600
Subject: [PATCH] the great onceification (libs)

Replace use of #ifndef header guards with #pragma once

Modern C++, baby!
---
 libs/ardour/ardour/amp.h                          | 4 +---
 libs/ardour/ardour/analyser.h                     | 4 +---
 libs/ardour/ardour/analysis_graph.h               | 4 +---
 libs/ardour/ardour/ardour.h                       | 4 +---
 libs/ardour/ardour/async_midi_port.h              | 4 +---
 libs/ardour/ardour/audio_backend.h                | 4 +---
 libs/ardour/ardour/audio_buffer.h                 | 4 +---
 libs/ardour/ardour/audio_library.h                | 4 +---
 libs/ardour/ardour/audio_playlist_importer.h      | 4 +---
 libs/ardour/ardour/audio_playlist_source.h        | 4 +---
 libs/ardour/ardour/audio_port.h                   | 4 +---
 libs/ardour/ardour/audio_region_importer.h        | 4 +---
 libs/ardour/ardour/audio_track.h                  | 4 +---
 libs/ardour/ardour/audio_track_importer.h         | 4 +---
 libs/ardour/ardour/audio_unit.h                   | 4 +---
 libs/ardour/ardour/audioanalyser.h                | 4 +---
 libs/ardour/ardour/audioengine.h                  | 4 +---
 libs/ardour/ardour/audiofile_tagger.h             | 4 +---
 libs/ardour/ardour/audiofilesource.h              | 4 +---
 libs/ardour/ardour/audioplaylist.h                | 4 +---
 libs/ardour/ardour/audioregion.h                  | 4 +---
 libs/ardour/ardour/audiorom.h                     | 4 +---
 libs/ardour/ardour/audiosource.h                  | 4 +---
 libs/ardour/ardour/auditioner.h                   | 4 +---
 libs/ardour/ardour/auto_bundle.h                  | 4 +---
 libs/ardour/ardour/automatable.h                  | 4 +---
 libs/ardour/ardour/automatable_sequence.h         | 4 +---
 libs/ardour/ardour/automation_control.h           | 4 +---
 libs/ardour/ardour/automation_list.h              | 4 +---
 libs/ardour/ardour/automation_watch.h             | 4 +---
 libs/ardour/ardour/beatbox.h                      | 4 +---
 libs/ardour/ardour/boost_debug.h                  | 4 +---
 libs/ardour/ardour/broadcast_info.h               | 4 +---
 libs/ardour/ardour/buffer.h                       | 4 +---
 libs/ardour/ardour/buffer_set.h                   | 4 +---
 libs/ardour/ardour/bundle.h                       | 4 +---
 libs/ardour/ardour/butler.h                       | 4 +---
 libs/ardour/ardour/caimportable.h                 | 4 +---
 libs/ardour/ardour/capturing_processor.h          | 4 +---
 libs/ardour/ardour/chan_count.h                   | 4 +---
 libs/ardour/ardour/chan_mapping.h                 | 4 +---
 libs/ardour/ardour/click.h                        | 4 +---
 libs/ardour/ardour/comparable_shared_ptr.h        | 4 +---
 libs/ardour/ardour/control_group.h                | 4 +---
 libs/ardour/ardour/control_group_member.h         | 4 +---
 libs/ardour/ardour/coreaudiosource.h              | 4 +---
 libs/ardour/ardour/cycle_timer.h                  | 4 +---
 libs/ardour/ardour/cycles.h                       | 4 +---
 libs/ardour/ardour/data_type.h                    | 4 +---
 libs/ardour/ardour/debug.h                        | 4 +---
 libs/ardour/ardour/delayline.h                    | 4 +---
 libs/ardour/ardour/delivery.h                     | 4 +---
 libs/ardour/ardour/directory_names.h              | 4 +---
 libs/ardour/ardour/disk_io.h                      | 4 +---
 libs/ardour/ardour/disk_writer.h                  | 4 +---
 libs/ardour/ardour/ebur128_analysis.h             | 4 +---
 libs/ardour/ardour/element_import_handler.h       | 4 +---
 libs/ardour/ardour/element_importer.h             | 4 +---
 libs/ardour/ardour/event_ring_buffer.h            | 4 +---
 libs/ardour/ardour/event_type_map.h               | 4 +---
 libs/ardour/ardour/export_analysis.h              | 4 +---
 libs/ardour/ardour/export_channel.h               | 4 +---
 libs/ardour/ardour/export_channel_configuration.h | 4 +---
 libs/ardour/ardour/export_failed.h                | 4 +---
 libs/ardour/ardour/export_filename.h              | 4 +---
 libs/ardour/ardour/export_format_base.h           | 4 +---
 libs/ardour/ardour/export_format_compatibility.h  | 4 +---
 libs/ardour/ardour/export_format_manager.h        | 4 +---
 libs/ardour/ardour/export_format_specification.h  | 4 +---
 libs/ardour/ardour/export_formats.h               | 4 +---
 libs/ardour/ardour/export_graph_builder.h         | 4 +---
 libs/ardour/ardour/export_handler.h               | 4 +---
 libs/ardour/ardour/export_pointers.h              | 4 +---
 libs/ardour/ardour/export_preset.h                | 4 +---
 libs/ardour/ardour/export_profile_manager.h       | 4 +---
 libs/ardour/ardour/export_status.h                | 4 +---
 libs/ardour/ardour/export_timespan.h              | 4 +---
 libs/ardour/ardour/file_source.h                  | 4 +---
 libs/ardour/ardour/filename_extensions.h          | 4 +---
 libs/ardour/ardour/filter.h                       | 4 +---
 libs/ardour/ardour/fixed_delay.h                  | 4 +---
 libs/ardour/ardour/gain_control.h                 | 4 +---
 libs/ardour/ardour/graph.h                        | 4 +---
 libs/ardour/ardour/graph_edges.h                  | 4 +---
 libs/ardour/ardour/graphnode.h                    | 4 +---
 libs/ardour/ardour/import_status.h                | 4 +---
 libs/ardour/ardour/importable_source.h            | 4 +---
 libs/ardour/ardour/instrument_info.h              | 4 +---
 libs/ardour/ardour/internal_return.h              | 4 +---
 libs/ardour/ardour/internal_send.h                | 4 +---
 libs/ardour/ardour/interthread_info.h             | 4 +---
 libs/ardour/ardour/io.h                           | 4 +---
 libs/ardour/ardour/io_processor.h                 | 4 +---
 libs/ardour/ardour/io_vector.h                    | 4 +---
 libs/ardour/ardour/ladspa_plugin.h                | 4 +---
 libs/ardour/ardour/latent.h                       | 4 +---
 libs/ardour/ardour/legatize.h                     | 4 +---
 libs/ardour/ardour/libardour_visibility.h         | 4 +---
 libs/ardour/ardour/library.h                      | 4 +---
 libs/ardour/ardour/linux_vst_support.h            | 4 +---
 libs/ardour/ardour/location.h                     | 4 +---
 libs/ardour/ardour/location_importer.h            | 4 +---
 libs/ardour/ardour/logcurve.h                     | 4 +---
 libs/ardour/ardour/logmeter.h                     | 4 +---
 libs/ardour/ardour/ltc_file_reader.h              | 4 +---
 libs/ardour/ardour/luabindings.h                  | 4 +---
 libs/ardour/ardour/luaproc.h                      | 4 +---
 libs/ardour/ardour/lxvst_plugin.h                 | 4 +---
 libs/ardour/ardour/mac_vst_plugin.h               | 4 +---
 libs/ardour/ardour/mac_vst_support.h              | 4 +---
 libs/ardour/ardour/meter.h                        | 4 +---
 libs/ardour/ardour/midi_automation_list_binder.h  | 4 +---
 libs/ardour/ardour/midi_buffer.h                  | 4 +---
 libs/ardour/ardour/midi_channel_filter.h          | 4 +---
 libs/ardour/ardour/midi_cursor.h                  | 4 +---
 libs/ardour/ardour/midi_model.h                   | 4 +---
 libs/ardour/ardour/midi_operator.h                | 4 +---
 libs/ardour/ardour/midi_playlist.h                | 4 +---
 libs/ardour/ardour/midi_port.h                    | 4 +---
 libs/ardour/ardour/midi_region.h                  | 4 +---
 libs/ardour/ardour/midi_ring_buffer.h             | 4 +---
 libs/ardour/ardour/midi_scene_change.h            | 4 +---
 libs/ardour/ardour/midi_scene_changer.h           | 4 +---
 libs/ardour/ardour/midi_source.h                  | 4 +---
 libs/ardour/ardour/midi_state_tracker.h           | 4 +---
 libs/ardour/ardour/midi_stretch.h                 | 4 +---
 libs/ardour/ardour/midi_track.h                   | 4 +---
 libs/ardour/ardour/midi_ui.h                      | 4 +---
 libs/ardour/ardour/mididm.h                       | 4 +---
 libs/ardour/ardour/midiport_manager.h             | 4 +---
 libs/ardour/ardour/mix.h                          | 4 +---
 libs/ardour/ardour/mode.h                         | 4 +---
 libs/ardour/ardour/monitor_control.h              | 4 +---
 libs/ardour/ardour/monitor_processor.h            | 4 +---
 libs/ardour/ardour/monitor_return.h               | 4 +---
 libs/ardour/ardour/monitorable.h                  | 4 +---
 libs/ardour/ardour/movable.h                      | 4 +---
 libs/ardour/ardour/msvc_libardour.h               | 4 +---
 libs/ardour/ardour/mtdm.h                         | 4 +---
 libs/ardour/ardour/mute_control.h                 | 4 +---
 libs/ardour/ardour/mute_master.h                  | 4 +---
 libs/ardour/ardour/muteable.h                     | 4 +---
 libs/ardour/ardour/onset_detector.h               | 4 +---
 libs/ardour/ardour/pan_controllable.h             | 4 +---
 libs/ardour/ardour/pannable.h                     | 4 +---
 libs/ardour/ardour/panner.h                       | 4 +---
 libs/ardour/ardour/panner_manager.h               | 4 +---
 libs/ardour/ardour/panner_shell.h                 | 4 +---
 libs/ardour/ardour/parameter_descriptor.h         | 4 +---
 libs/ardour/ardour/parameter_types.h              | 4 +---
 libs/ardour/ardour/peak.h                         | 4 +---
 libs/ardour/ardour/phase_control.h                | 4 +---
 libs/ardour/ardour/pitch.h                        | 4 +---
 libs/ardour/ardour/playlist.h                     | 4 +---
 libs/ardour/ardour/playlist_factory.h             | 4 +---
 libs/ardour/ardour/playlist_source.h              | 4 +---
 libs/ardour/ardour/plugin.h                       | 4 +---
 libs/ardour/ardour/plugin_insert.h                | 4 +---
 libs/ardour/ardour/plugin_manager.h               | 4 +---
 libs/ardour/ardour/plugin_types.h                 | 5 ++---
 libs/ardour/ardour/port.h                         | 4 +---
 libs/ardour/ardour/port_engine.h                  | 4 +---
 libs/ardour/ardour/port_insert.h                  | 4 +---
 libs/ardour/ardour/port_manager.h                 | 4 +---
 libs/ardour/ardour/port_set.h                     | 4 +---
 libs/ardour/ardour/presentation_info.h            | 4 +---
 libs/ardour/ardour/processor.h                    | 4 +---
 libs/ardour/ardour/profile.h                      | 4 +---
 libs/ardour/ardour/proxy_controllable.h           | 4 +---
 libs/ardour/ardour/quantize.h                     | 4 +---
 libs/ardour/ardour/rb_effect.h                    | 4 +---
 libs/ardour/ardour/rc_configuration.h             | 4 +---
 libs/ardour/ardour/readable.h                     | 4 +---
 libs/ardour/ardour/readonly_control.h             | 4 +---
 libs/ardour/ardour/recent_sessions.h              | 4 +---
 libs/ardour/ardour/record_enable_control.h        | 4 +---
 libs/ardour/ardour/record_safe_control.h          | 4 +---
 libs/ardour/ardour/recordable.h                   | 4 +---
 libs/ardour/ardour/region.h                       | 4 +---
 libs/ardour/ardour/region_factory.h               | 4 +---
 libs/ardour/ardour/region_fx_plugin.h             | 4 +---
 libs/ardour/ardour/region_sorters.h               | 4 +---
 libs/ardour/ardour/resampled_source.h             | 4 +---
 libs/ardour/ardour/return.h                       | 4 +---
 libs/ardour/ardour/reverse.h                      | 4 +---
 libs/ardour/ardour/revision.h                     | 4 +---
 libs/ardour/ardour/route.h                        | 4 +---
 libs/ardour/ardour/route_group.h                  | 4 +---
 libs/ardour/ardour/route_group_member.h           | 4 +---
 libs/ardour/ardour/route_group_specialized.h      | 4 +---
 libs/ardour/ardour/rt_midibuffer.h                | 4 +---
 libs/ardour/ardour/runtime_functions.h            | 4 +---
 libs/ardour/ardour/scene_change.h                 | 4 +---
 libs/ardour/ardour/scene_changer.h                | 4 +---
 libs/ardour/ardour/search_paths.h                 | 4 +---
 libs/ardour/ardour/segment_descriptor.h           | 4 +---
 libs/ardour/ardour/selection.h                    | 4 +---
 libs/ardour/ardour/send.h                         | 4 +---
 libs/ardour/ardour/session.h                      | 4 +---
 libs/ardour/ardour/session_configuration.h        | 4 +---
 libs/ardour/ardour/session_directory.h            | 4 +---
 libs/ardour/ardour/session_event.h                | 4 +---
 libs/ardour/ardour/session_handle.h               | 4 +---
 libs/ardour/ardour/session_metadata.h             | 4 +---
 libs/ardour/ardour/session_object.h               | 4 +---
 libs/ardour/ardour/session_playlist.h             | 4 +---
 libs/ardour/ardour/session_playlists.h            | 4 +---
 libs/ardour/ardour/session_route.h                | 4 +---
 libs/ardour/ardour/session_utils.h                | 4 +---
 libs/ardour/ardour/sidechain.h                    | 4 +---
 libs/ardour/ardour/silentfilesource.h             | 4 +---
 libs/ardour/ardour/slavable.h                     | 4 +---
 libs/ardour/ardour/slavable_automation_control.h  | 4 +---
 libs/ardour/ardour/smf_source.h                   | 4 +---
 libs/ardour/ardour/sndfile_helpers.h              | 4 +---
 libs/ardour/ardour/sndfileimportable.h            | 4 +---
 libs/ardour/ardour/sndfilesource.h                | 4 +---
 libs/ardour/ardour/solo_control.h                 | 4 +---
 libs/ardour/ardour/solo_isolate_control.h         | 4 +---
 libs/ardour/ardour/solo_safe_control.h            | 4 +---
 libs/ardour/ardour/soloable.h                     | 4 +---
 libs/ardour/ardour/soundcloud_upload.h            | 4 +---
 libs/ardour/ardour/soundseq.h                     | 4 +---
 libs/ardour/ardour/source.h                       | 4 +---
 libs/ardour/ardour/source_factory.h               | 4 +---
 libs/ardour/ardour/speaker.h                      | 4 +---
 libs/ardour/ardour/speakers.h                     | 4 +---
 libs/ardour/ardour/spline.h                       | 4 +---
 libs/ardour/ardour/srcfilesource.h                | 4 +---
 libs/ardour/ardour/step_sequencer.h               | 4 +---
 libs/ardour/ardour/stretch.h                      | 4 +---
 libs/ardour/ardour/stripable.h                    | 4 +---
 libs/ardour/ardour/surround_return.h              | 4 +---
 libs/ardour/ardour/surround_send.h                | 4 +---
 libs/ardour/ardour/tailtime.h                     | 4 +---
 libs/ardour/ardour/tempo.h                        | 4 +---
 libs/ardour/ardour/tempo_map_importer.h           | 4 +---
 libs/ardour/ardour/thawlist.h                     | 5 ++---
 libs/ardour/ardour/ticker.h                       | 4 +---
 libs/ardour/ardour/timecode.h                     | 4 +---
 libs/ardour/ardour/timefx_request.h               | 4 +---
 libs/ardour/ardour/timestamps.h                   | 4 +---
 libs/ardour/ardour/track.h                        | 4 +---
 libs/ardour/ardour/transform.h                    | 4 +---
 libs/ardour/ardour/transient_detector.h           | 4 +---
 libs/ardour/ardour/transport_master.h             | 4 +---
 libs/ardour/ardour/transport_master_manager.h     | 4 +---
 libs/ardour/ardour/transpose.h                    | 4 +---
 libs/ardour/ardour/triggerbox.h                   | 4 +---
 libs/ardour/ardour/trimmable.h                    | 4 +---
 libs/ardour/ardour/types.h                        | 4 +---
 libs/ardour/ardour/unknown_processor.h            | 4 +---
 libs/ardour/ardour/uri_map.h                      | 4 +---
 libs/ardour/ardour/user_bundle.h                  | 4 +---
 libs/ardour/ardour/utils.h                        | 4 +---
 libs/ardour/ardour/value_as_string.h              | 4 +---
 libs/ardour/ardour/variant.h                      | 4 +---
 libs/ardour/ardour/vca.h                          | 4 +---
 libs/ardour/ardour/vca_manager.h                  | 4 +---
 libs/ardour/ardour/velocity_control.h             | 4 +---
 libs/ardour/ardour/vst_plugin.h                   | 4 +---
 libs/ardour/ardour/vst_types.h                    | 4 +---
 libs/ardour/ardour/windows_vst_plugin.h           | 4 +---
 libs/ardour/ardour/worker.h                       | 4 +---
 libs/ardour/ardour/wrong_program.h                | 4 +---
 libs/ardouralsautil/ardouralsautil/deviceinfo.h   | 4 +---
 libs/ardouralsautil/ardouralsautil/devicelist.h   | 4 +---
 libs/audiographer/audiographer/visibility.h       | 4 +---
 libs/evoral/evoral/visibility.h                   | 4 +---
 libs/gtkmm2ext/gtkmm2ext/doi.h                    | 4 +---
 libs/gtkmm2ext/gtkmm2ext/gtk_ui.h                 | 4 +---
 libs/gtkmm2ext/gtkmm2ext/gtkutils.h               | 4 +---
 libs/gtkmm2ext/gtkmm2ext/gui_thread.h             | 4 +---
 libs/gtkmm2ext/gtkmm2ext/textviewer.h             | 4 +---
 libs/midi++2/midi++/channel.h                     | 4 +---
 libs/midi++2/midi++/events.h                      | 4 +---
 libs/midi++2/midi++/ipmidi_port.h                 | 4 +---
 libs/midi++2/midi++/libmidi_visibility.h          | 4 +---
 libs/midi++2/midi++/mmc.h                         | 4 +---
 libs/midi++2/midi++/parser.h                      | 4 +---
 libs/midi++2/midi++/port.h                        | 4 +---
 libs/midi++2/midi++/types.h                       | 4 +---
 libs/pbd/pbd/abstract_ui.h                        | 4 +---
 libs/pbd/pbd/assert.h                             | 4 +---
 libs/pbd/pbd/atomic.h                             | 4 +---
 libs/pbd/pbd/base_ui.h                            | 4 +---
 libs/pbd/pbd/basename.h                           | 4 +---
 libs/pbd/pbd/boost_debug.h                        | 4 +---
 libs/pbd/pbd/cartesian.h                          | 4 +---
 libs/pbd/pbd/command.h                            | 4 +---
 libs/pbd/pbd/configuration.h                      | 4 +---
 libs/pbd/pbd/configuration_variable.h             | 4 +---
 libs/pbd/pbd/control_math.h                       | 4 +---
 libs/pbd/pbd/controllable.h                       | 4 +---
 libs/pbd/pbd/convert.h                            | 4 +---
 libs/pbd/pbd/cpus.h                               | 4 +---
 libs/pbd/pbd/crossthread.h                        | 4 +---
 libs/pbd/pbd/debug.h                              | 4 +---
 libs/pbd/pbd/debug_rt_alloc.h                     | 5 +----
 libs/pbd/pbd/demangle.h                           | 4 +---
 libs/pbd/pbd/destructible.h                       | 4 +---
 libs/pbd/pbd/downloader.h                         | 4 +---
 libs/pbd/pbd/enumwriter.h                         | 4 +---
 libs/pbd/pbd/epa.h                                | 4 +---
 libs/pbd/pbd/error.h                              | 4 +---
 libs/pbd/pbd/event_loop.h                         | 4 +---
 libs/pbd/pbd/failed_constructor.h                 | 4 +---
 libs/pbd/pbd/fastlog.h                            | 4 +---
 libs/pbd/pbd/ffs.h                                | 4 +---
 libs/pbd/pbd/floating.h                           | 4 +---
 libs/pbd/pbd/fpu.h                                | 4 +---
 libs/pbd/pbd/functor_command.h                    | 4 +---
 libs/pbd/pbd/glib_event_source.h                  | 4 +---
 libs/pbd/pbd/gstdio_compat.h                      | 4 +---
 libs/pbd/pbd/history_owner.h                      | 4 +---
 libs/pbd/pbd/id.h                                 | 4 +---
 libs/pbd/pbd/inflater.h                           | 4 +---
 libs/pbd/pbd/integer_division.h                   | 4 +---
 libs/pbd/pbd/libpbd_visibility.h                  | 4 +---
 libs/pbd/pbd/malign.h                             | 4 +---
 libs/pbd/pbd/match.h                              | 4 +---
 libs/pbd/pbd/mathfix.h                            | 4 +---
 libs/pbd/pbd/memento_command.h                    | 4 +---
 libs/pbd/pbd/microseconds.h                       | 4 +---
 libs/pbd/pbd/mountpoint.h                         | 4 +---
 libs/pbd/pbd/openuri.h                            | 4 +---
 libs/pbd/pbd/pathexpand.h                         | 4 +---
 libs/pbd/pbd/pbd.h                                | 4 +---
 libs/pbd/pbd/playback_buffer.h                    | 4 +---
 libs/pbd/pbd/pool.h                               | 4 +---
 libs/pbd/pbd/properties.h                         | 4 +---
 libs/pbd/pbd/property_basics.h                    | 4 +---
 libs/pbd/pbd/property_basics_impl.h               | 4 +---
 libs/pbd/pbd/property_list.h                      | 4 +---
 libs/pbd/pbd/property_list_impl.h                 | 4 +---
 libs/pbd/pbd/rcu.h                                | 4 +---
 libs/pbd/pbd/receiver.h                           | 4 +---
 libs/pbd/pbd/replace_all.h                        | 4 +---
 libs/pbd/pbd/ringbuffer.h                         | 4 +---
 libs/pbd/pbd/ringbufferNPT.h                      | 4 +---
 libs/pbd/pbd/scoped_file_descriptor.h             | 4 +---
 libs/pbd/pbd/search_path.h                        | 4 +---
 libs/pbd/pbd/selectable.h                         | 4 +---
 libs/pbd/pbd/semutils.h                           | 4 +---
 libs/pbd/pbd/sequence_property.h                  | 4 +---
 libs/pbd/pbd/shortpath.h                          | 4 +---
 libs/pbd/pbd/signals.h                            | 4 +---
 libs/pbd/pbd/stacktrace.h                         | 4 +---
 libs/pbd/pbd/stateful.h                           | 4 +---
 libs/pbd/pbd/stateful_diff_command.h              | 4 +---
 libs/pbd/pbd/statefuldestructible.h               | 4 +---
 libs/pbd/pbd/stl_delete.h                         | 4 +---
 libs/pbd/pbd/strsplit.h                           | 4 +---
 libs/pbd/pbd/textreceiver.h                       | 4 +---
 libs/pbd/pbd/thrown_error.h                       | 4 +---
 libs/pbd/pbd/timer.h                              | 4 +---
 libs/pbd/pbd/timing.h                             | 4 +---
 libs/pbd/pbd/touchable.h                          | 4 +---
 libs/pbd/pbd/transmitter.h                        | 4 +---
 libs/pbd/pbd/undo.h                               | 4 +---
 libs/pbd/pbd/unknown_type.h                       | 4 +---
 libs/pbd/pbd/unwind.h                             | 4 +---
 libs/pbd/pbd/uuid.h                               | 4 +---
 libs/pbd/pbd/uuid_boost.h                         | 4 +---
 libs/pbd/pbd/whitespace.h                         | 4 +---
 libs/pbd/pbd/windows_special_dirs.h               | 4 +---
 libs/temporal/temporal/bbt_argument.h             | 4 +---
 libs/temporal/temporal/bbt_time.h                 | 4 +---
 libs/temporal/temporal/debug.h                    | 4 +---
 libs/temporal/temporal/domain_provider.h          | 4 +---
 libs/temporal/temporal/domain_swap.h              | 4 +---
 libs/temporal/temporal/superclock.h               | 4 +---
 libs/temporal/temporal/tempo.h                    | 4 +---
 libs/temporal/temporal/time.h                     | 4 +---
 libs/temporal/temporal/timeline.h                 | 4 +---
 libs/temporal/temporal/types.h                    | 4 +---
 libs/temporal/temporal/visibility.h               | 4 +---
 libs/waveview/waveview/visibility.h               | 4 +---
 libs/widgets/widgets/visibility.h                 | 4 +---
 379 files changed, 381 insertions(+), 1138 deletions(-)

diff --git a/libs/ardour/ardour/amp.h b/libs/ardour/ardour/amp.h
index 1eb1880523..7fe29f5cf9 100644
--- a/libs/ardour/ardour/amp.h
+++ b/libs/ardour/ardour/amp.h
@@ -19,8 +19,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_amp_h__
-#define __ardour_amp_h__
+#pragma once
 
 #include "ardour/dB.h"
 #include "ardour/libardour_visibility.h"
@@ -88,4 +87,3 @@ private:
 
 } // namespace ARDOUR
 
-#endif // __ardour_amp_h__
diff --git a/libs/ardour/ardour/analyser.h b/libs/ardour/ardour/analyser.h
index de678b14cf..699983f1d9 100644
--- a/libs/ardour/ardour/analyser.h
+++ b/libs/ardour/ardour/analyser.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_analyser_h__
-#define __ardour_analyser_h__
+#pragma once
 
 #include <memory>
 
@@ -54,4 +53,3 @@ private:
 
 } // namespace ARDOUR
 
-#endif /* __ardour_analyser_h__ */
diff --git a/libs/ardour/ardour/analysis_graph.h b/libs/ardour/ardour/analysis_graph.h
index 48b354501c..ad9fb0fc0d 100644
--- a/libs/ardour/ardour/analysis_graph.h
+++ b/libs/ardour/ardour/analysis_graph.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_analysis_graph_h__
-#define __ardour_analysis_graph_h__
+#pragma once
 
 #include <map>
 #include <memory>
@@ -82,4 +81,3 @@ class LIBARDOUR_API AnalysisGraph {
 		AnalysisPtr     analyser;
 };
 } // namespace ARDOUR
-#endif
diff --git a/libs/ardour/ardour/ardour.h b/libs/ardour/ardour/ardour.h
index d200e4eed3..43abeb99af 100644
--- a/libs/ardour/ardour/ardour.h
+++ b/libs/ardour/ardour/ardour.h
@@ -21,8 +21,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_ardour_h__
-#define __ardour_ardour_h__
+#pragma once
 
 #include <map>
 #include <string>
@@ -99,5 +98,4 @@ namespace ARDOUR {
 	LIBARDOUR_API void reset_performance_meters (Session*);
 }
 
-#endif /* __ardour_ardour_h__ */
 
diff --git a/libs/ardour/ardour/async_midi_port.h b/libs/ardour/ardour/async_midi_port.h
index fdc7c1ffad..d7fb9248d8 100644
--- a/libs/ardour/ardour/async_midi_port.h
+++ b/libs/ardour/ardour/async_midi_port.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef  __libardour_async_midiport_h__
-#define  __libardour_async_midiport_h__
+#pragma once
 
 #include <string>
 #include <iostream>
@@ -108,4 +107,3 @@ class LIBARDOUR_API AsyncMIDIPort : public ARDOUR::MidiPort, public MIDI::Port {
 
 } // namespace ARDOUR
 
-#endif /* __libardour_async_midiport_h__ */
diff --git a/libs/ardour/ardour/audio_backend.h b/libs/ardour/ardour/audio_backend.h
index 5986b895e4..4d9140ddfb 100644
--- a/libs/ardour/ardour/audio_backend.h
+++ b/libs/ardour/ardour/audio_backend.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libardour_audiobackend_h__
-#define __libardour_audiobackend_h__
+#pragma once
 
 #include <string>
 #include <vector>
@@ -841,4 +840,3 @@ protected:
 
 } // namespace ARDOUR
 
-#endif /* __libardour_audiobackend_h__ */
diff --git a/libs/ardour/ardour/audio_buffer.h b/libs/ardour/ardour/audio_buffer.h
index bec4bdd7cc..d891e6d9fa 100644
--- a/libs/ardour/ardour/audio_buffer.h
+++ b/libs/ardour/ardour/audio_buffer.h
@@ -19,8 +19,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_audio_buffer_h__
-#define __ardour_audio_buffer_h__
+#pragma once
 
 #include <cstring>
 
@@ -268,4 +267,3 @@ private:
 
 } // namespace ARDOUR
 
-#endif // __ardour_audio_audio_buffer_h__
diff --git a/libs/ardour/ardour/audio_library.h b/libs/ardour/ardour/audio_library.h
index 6c495a80ce..8d7892f9a3 100644
--- a/libs/ardour/ardour/audio_library.h
+++ b/libs/ardour/ardour/audio_library.h
@@ -19,8 +19,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_audio_library_h__
-#define __ardour_audio_library_h__
+#pragma once
 
 #include <string>
 #include <map>
@@ -51,4 +50,3 @@ LIBARDOUR_API extern AudioLibrary* Library;
 
 } // ARDOUR namespace
 
-#endif // __ardour_audio_library_h__
diff --git a/libs/ardour/ardour/audio_playlist_importer.h b/libs/ardour/ardour/audio_playlist_importer.h
index ee767e63fd..3652e1de53 100644
--- a/libs/ardour/ardour/audio_playlist_importer.h
+++ b/libs/ardour/ardour/audio_playlist_importer.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_audio_playlist_importer_h__
-#define __ardour_audio_playlist_importer_h__
+#pragma once
 
 #include <list>
 #include <memory>
@@ -96,4 +95,3 @@ class LIBARDOUR_API AudioPlaylistImporter : public ElementImporter
 
 } // namespace ARDOUR
 
-#endif
diff --git a/libs/ardour/ardour/audio_playlist_source.h b/libs/ardour/ardour/audio_playlist_source.h
index f973dfa4d0..e2eeb78a8d 100644
--- a/libs/ardour/ardour/audio_playlist_source.h
+++ b/libs/ardour/ardour/audio_playlist_source.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_audio_playlist_source_h__
-#define __ardour_audio_playlist_source_h__
+#pragma once
 
 #include <memory>
 #include <string>
@@ -69,4 +68,3 @@ private:
 
 } /* namespace */
 
-#endif /* __ardour_audio_playlist_source_h__ */
diff --git a/libs/ardour/ardour/audio_port.h b/libs/ardour/ardour/audio_port.h
index ce699e0010..1af5c44b00 100644
--- a/libs/ardour/ardour/audio_port.h
+++ b/libs/ardour/ardour/audio_port.h
@@ -19,8 +19,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_audio_port_h__
-#define __ardour_audio_port_h__
+#pragma once
 
 #include "zita-resampler/vmresampler.h"
 
@@ -71,4 +70,3 @@ private:
 
 } // namespace ARDOUR
 
-#endif /* __ardour_audio_port_h__ */
diff --git a/libs/ardour/ardour/audio_region_importer.h b/libs/ardour/ardour/audio_region_importer.h
index ba52627539..043ee6f611 100644
--- a/libs/ardour/ardour/audio_region_importer.h
+++ b/libs/ardour/ardour/audio_region_importer.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_audio_region_importer_h__
-#define __ardour_audio_region_importer_h__
+#pragma once
 
 #include <list>
 #include <map>
@@ -109,4 +108,3 @@ class LIBARDOUR_API AudioRegionImporter : public ElementImporter
 
 } // namespace ARDOUR
 
-#endif
diff --git a/libs/ardour/ardour/audio_track.h b/libs/ardour/ardour/audio_track.h
index a367a34af6..b813d91314 100644
--- a/libs/ardour/ardour/audio_track.h
+++ b/libs/ardour/ardour/audio_track.h
@@ -19,8 +19,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_audio_track_h__
-#define __ardour_audio_track_h__
+#pragma once
 
 #include "ardour/interthread_info.h"
 #include "ardour/track.h"
@@ -64,4 +63,3 @@ class LIBARDOUR_API AudioTrack : public Track
 
 } // namespace ARDOUR
 
-#endif /* __ardour_audio_track_h__ */
diff --git a/libs/ardour/ardour/audio_track_importer.h b/libs/ardour/ardour/audio_track_importer.h
index ea5a97152e..42cf4f28e0 100644
--- a/libs/ardour/ardour/audio_track_importer.h
+++ b/libs/ardour/ardour/audio_track_importer.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_audio_track_importer_h__
-#define __ardour_audio_track_importer_h__
+#pragma once
 
 #include <list>
 
@@ -84,4 +83,3 @@ class LIBARDOUR_API AudioTrackImporter : public ElementImporter
 
 } // namespace ARDOUR
 
-#endif
diff --git a/libs/ardour/ardour/audio_unit.h b/libs/ardour/ardour/audio_unit.h
index 6ce63b00c9..bac73b9e7d 100644
--- a/libs/ardour/ardour/audio_unit.h
+++ b/libs/ardour/ardour/audio_unit.h
@@ -19,8 +19,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_audio_unit_h__
-#define __ardour_audio_unit_h__
+#pragma once
 
 #include <atomic>
 #include <cstdint>
@@ -272,4 +271,3 @@ typedef std::shared_ptr<AUPluginInfo> AUPluginInfoPtr;
 
 } // namespace ARDOUR
 
-#endif // __ardour_audio_unit_h__
diff --git a/libs/ardour/ardour/audioanalyser.h b/libs/ardour/ardour/audioanalyser.h
index 283910ea61..912d980289 100644
--- a/libs/ardour/ardour/audioanalyser.h
+++ b/libs/ardour/ardour/audioanalyser.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_audioanalyser_h__
-#define __ardour_audioanalyser_h__
+#pragma once
 
 #include <vector>
 #include <string>
@@ -72,4 +71,3 @@ class LIBARDOUR_API AudioAnalyser : public boost::noncopyable {
 
 } /* namespace */
 
-#endif /* __ardour_audioanalyser_h__ */
diff --git a/libs/ardour/ardour/audioengine.h b/libs/ardour/ardour/audioengine.h
index cc1b0db6bc..3941396ee6 100644
--- a/libs/ardour/ardour/audioengine.h
+++ b/libs/ardour/ardour/audioengine.h
@@ -20,8 +20,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_audioengine_h__
-#define __ardour_audioengine_h__
+#pragma once
 
 #ifdef WAF_BUILD
 #include "libardour-config.h"
@@ -329,4 +328,3 @@ class LIBARDOUR_API AudioEngine : public PortManager, public SessionHandlePtr
 
 } // namespace ARDOUR
 
-#endif /* __ardour_audioengine_h__ */
diff --git a/libs/ardour/ardour/audiofile_tagger.h b/libs/ardour/ardour/audiofile_tagger.h
index 7a299dbdd3..0b76611207 100644
--- a/libs/ardour/ardour/audiofile_tagger.h
+++ b/libs/ardour/ardour/audiofile_tagger.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_audiofile_tagger_h__
-#define __ardour_audiofile_tagger_h__
+#pragma once
 
 #include <string>
 
@@ -51,4 +50,3 @@ private:
 
 } // namespace ARDOUR
 
-#endif /* __ardour_audiofile_tagger_h__ */
diff --git a/libs/ardour/ardour/audiofilesource.h b/libs/ardour/ardour/audiofilesource.h
index 614b26d279..2ccbad390b 100644
--- a/libs/ardour/ardour/audiofilesource.h
+++ b/libs/ardour/ardour/audiofilesource.h
@@ -20,8 +20,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_audiofilesource_h__
-#define __ardour_audiofilesource_h__
+#pragma once
 
 #include <exception>
 #include <time.h>
@@ -117,5 +116,4 @@ protected:
 
 } // namespace ARDOUR
 
-#endif /* __ardour_audiofilesource_h__ */
 
diff --git a/libs/ardour/ardour/audioplaylist.h b/libs/ardour/ardour/audioplaylist.h
index f85506c780..d9e5c1cc74 100644
--- a/libs/ardour/ardour/audioplaylist.h
+++ b/libs/ardour/ardour/audioplaylist.h
@@ -19,8 +19,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_audio_playlist_h__
-#define __ardour_audio_playlist_h__
+#pragma once
 
 #include <vector>
 #include <list>
@@ -63,4 +62,3 @@ private:
 
 } /* namespace ARDOUR */
 
-#endif /* __ardour_audio_playlist_h__ */
diff --git a/libs/ardour/ardour/audioregion.h b/libs/ardour/ardour/audioregion.h
index 07a6e99dec..182c001703 100644
--- a/libs/ardour/ardour/audioregion.h
+++ b/libs/ardour/ardour/audioregion.h
@@ -20,8 +20,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_audio_region_h__
-#define __ardour_audio_region_h__
+#pragma once
 
 #include <atomic>
 #include <vector>
@@ -301,4 +300,3 @@ extern "C" {
 	LIBARDOUR_API uint32_t sourcefile_length_from_c (void *arg, double);
 }
 
-#endif /* __ardour_audio_region_h__ */
diff --git a/libs/ardour/ardour/audiorom.h b/libs/ardour/ardour/audiorom.h
index 248ed3f9bc..03e7f941c3 100644
--- a/libs/ardour/ardour/audiorom.h
+++ b/libs/ardour/ardour/audiorom.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_audio_rom_h__
-#define __ardour_audio_rom_h__
+#pragma once
 
 #include "ardour/libardour_visibility.h"
 #include "ardour/readable.h"
@@ -47,4 +46,3 @@ private:
 
 }
 
-#endif /* __ardour_readable_h__ */
diff --git a/libs/ardour/ardour/audiosource.h b/libs/ardour/ardour/audiosource.h
index de1c612980..96f4938e3f 100644
--- a/libs/ardour/ardour/audiosource.h
+++ b/libs/ardour/ardour/audiosource.h
@@ -20,8 +20,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_audio_source_h__
-#define __ardour_audio_source_h__
+#pragma once
 
 #include <memory>
 
@@ -162,4 +161,3 @@ class LIBARDOUR_API AudioSource : virtual public Source, public ARDOUR::AudioRea
 
 }
 
-#endif /* __ardour_audio_source_h__ */
diff --git a/libs/ardour/ardour/auditioner.h b/libs/ardour/ardour/auditioner.h
index 02b44bc5c5..76c1d30b09 100644
--- a/libs/ardour/ardour/auditioner.h
+++ b/libs/ardour/ardour/auditioner.h
@@ -20,8 +20,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_auditioner_h__
-#define __ardour_auditioner_h__
+#pragma once
 
 #include <string>
 
@@ -141,4 +140,3 @@ private:
 
 }; /* namespace ARDOUR */
 
-#endif /* __ardour_auditioner_h__ */
diff --git a/libs/ardour/ardour/auto_bundle.h b/libs/ardour/ardour/auto_bundle.h
index 589590a337..2a49575023 100644
--- a/libs/ardour/ardour/auto_bundle.h
+++ b/libs/ardour/ardour/auto_bundle.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_auto_bundle_h__
-#define __ardour_auto_bundle_h__
+#pragma once
 
 #include <vector>
 #include <glibmm/threads.h>
@@ -43,4 +42,3 @@ class LIBARDOUR_API AutoBundle : public Bundle {
 
 }
 
-#endif /* __ardour_auto_bundle_h__ */
diff --git a/libs/ardour/ardour/automatable.h b/libs/ardour/ardour/automatable.h
index 10d31bc127..3b0fb9f35b 100644
--- a/libs/ardour/ardour/automatable.h
+++ b/libs/ardour/ardour/automatable.h
@@ -19,8 +19,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_automatable_h__
-#define __ardour_automatable_h__
+#pragma once
 
 #include <map>
 #include <memory>
@@ -149,4 +148,3 @@ private:
 
 } // namespace ARDOUR
 
-#endif /* __ardour_automatable_h__ */
diff --git a/libs/ardour/ardour/automatable_sequence.h b/libs/ardour/ardour/automatable_sequence.h
index a01a35d627..9812c93271 100644
--- a/libs/ardour/ardour/automatable_sequence.h
+++ b/libs/ardour/ardour/automatable_sequence.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_automatable_sequence_h__
-#define __ardour_automatable_sequence_h__
+#pragma once
 
 #include "evoral/Sequence.h"
 #include "ardour/automatable.h"
@@ -46,5 +45,4 @@ public:
 
 } // namespace ARDOUR
 
-#endif /* __ardour_automatable_sequence_h__ */
 
diff --git a/libs/ardour/ardour/automation_control.h b/libs/ardour/ardour/automation_control.h
index 8c10d407c1..f7053feca2 100644
--- a/libs/ardour/ardour/automation_control.h
+++ b/libs/ardour/ardour/automation_control.h
@@ -20,8 +20,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_automation_control_h__
-#define __ardour_automation_control_h__
+#pragma once
 
 #include <map>
 #include <memory>
@@ -180,4 +179,3 @@ private:
 
 } // namespace ARDOUR
 
-#endif /* __ardour_automation_control_h__ */
diff --git a/libs/ardour/ardour/automation_list.h b/libs/ardour/ardour/automation_list.h
index 5d025e7517..2115d4b356 100644
--- a/libs/ardour/ardour/automation_list.h
+++ b/libs/ardour/ardour/automation_list.h
@@ -20,8 +20,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_automation_event_h__
-#define __ardour_automation_event_h__
+#pragma once
 
 #include <atomic>
 #include <cstdint>
@@ -147,4 +146,3 @@ private:
 
 } // namespace
 
-#endif /* __ardour_automation_event_h__ */
diff --git a/libs/ardour/ardour/automation_watch.h b/libs/ardour/ardour/automation_watch.h
index 71756f24da..409834ce6c 100644
--- a/libs/ardour/ardour/automation_watch.h
+++ b/libs/ardour/ardour/automation_watch.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_automation_watch_h__
-#define __ardour_automation_watch_h__
+#pragma once
 
 #include <memory>
 #include <set>
@@ -70,4 +69,3 @@ private:
 
 } /* namespace */
 
-#endif // __ardour_automation_watch_h__
diff --git a/libs/ardour/ardour/beatbox.h b/libs/ardour/ardour/beatbox.h
index e8dd62c12d..a9e57dd8af 100644
--- a/libs/ardour/ardour/beatbox.h
+++ b/libs/ardour/ardour/beatbox.h
@@ -17,8 +17,7 @@
 
 */
 
-#ifndef __ardour_beatbox_h__
-#define __ardour_beatbox_h__
+#pragma once
 
 #include <algorithm>
 #include <vector>
@@ -71,4 +70,3 @@ class BeatBox : public ARDOUR::Processor {
 
 } /* namespace */
 
-#endif /* __ardour_beatbox_h__ */
diff --git a/libs/ardour/ardour/boost_debug.h b/libs/ardour/ardour/boost_debug.h
index 132c17cd02..3bbd059918 100644
--- a/libs/ardour/ardour/boost_debug.h
+++ b/libs/ardour/ardour/boost_debug.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libardour_boost_debug_h__
-#define __libardour_boost_debug_h__
+#pragma once
 
 #include "pbd/boost_debug.h"
 
@@ -45,4 +44,3 @@
 #define BOOST_SHOW_POINTERS()
 #endif
 
-#endif /* __libardour_boost_debug_h__ */
diff --git a/libs/ardour/ardour/broadcast_info.h b/libs/ardour/ardour/broadcast_info.h
index bd7847c1a5..326e0e85f0 100644
--- a/libs/ardour/ardour/broadcast_info.h
+++ b/libs/ardour/ardour/broadcast_info.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_broadcast_info_h__
-#define __ardour_broadcast_info_h__
+#pragma once
 
 #include <string>
 
@@ -46,4 +45,3 @@ class LIBARDOUR_API BroadcastInfo : public AudioGrapher::BroadcastInfo
 
 } // namespace ARDOUR
 
-#endif /* __ardour_broadcast_info_h__ */
diff --git a/libs/ardour/ardour/buffer.h b/libs/ardour/ardour/buffer.h
index 14a406d736..bb95968ef5 100644
--- a/libs/ardour/ardour/buffer.h
+++ b/libs/ardour/ardour/buffer.h
@@ -19,8 +19,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_buffer_h__
-#define __ardour_buffer_h__
+#pragma once
 
 #include <stddef.h>
 
@@ -91,4 +90,3 @@ public:
 
 } // namespace ARDOUR
 
-#endif // __ardour_buffer_h__
diff --git a/libs/ardour/ardour/buffer_set.h b/libs/ardour/ardour/buffer_set.h
index 95b40958f5..2e17c10086 100644
--- a/libs/ardour/ardour/buffer_set.h
+++ b/libs/ardour/ardour/buffer_set.h
@@ -19,8 +19,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_buffer_set_h__
-#define __ardour_buffer_set_h__
+#pragma once
 
 #ifdef WAF_BUILD
 #include "libardour-config.h"
@@ -229,4 +228,3 @@ private:
 
 } // namespace ARDOUR
 
-#endif // __ardour_buffer_set_h__
diff --git a/libs/ardour/ardour/bundle.h b/libs/ardour/ardour/bundle.h
index 49c8ffc6f0..9c4c91a1f1 100644
--- a/libs/ardour/ardour/bundle.h
+++ b/libs/ardour/ardour/bundle.h
@@ -19,8 +19,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_bundle_h__
-#define __ardour_bundle_h__
+#pragma once
 
 #include <memory>
 #include <string>
@@ -183,4 +182,3 @@ public:
 
 std::ostream & operator<< (std::ostream & o, ARDOUR::Bundle const &);
 
-#endif /* __ardour_bundle_h__ */
diff --git a/libs/ardour/ardour/butler.h b/libs/ardour/ardour/butler.h
index 7c7d33f62c..b56997786b 100644
--- a/libs/ardour/ardour/butler.h
+++ b/libs/ardour/ardour/butler.h
@@ -20,8 +20,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_butler_h__
-#define __ardour_butler_h__
+#pragma once
 
 #include <atomic>
 
@@ -122,4 +121,3 @@ private:
 
 } // namespace ARDOUR
 
-#endif // __ardour_butler_h__
diff --git a/libs/ardour/ardour/caimportable.h b/libs/ardour/ardour/caimportable.h
index f39a84a38c..9c78cedec3 100644
--- a/libs/ardour/ardour/caimportable.h
+++ b/libs/ardour/ardour/caimportable.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_ca_importable_source_h__
-#define __ardour_ca_importable_source_h__
+#pragma once
 
 #include "pbd/failed_constructor.h"
 #include "ardour/libardour_visibility.h"
@@ -56,4 +55,3 @@ class LIBARDOUR_API CAImportableSource : public ImportableSource {
 
 }
 
-#endif /* __ardour_ca_importable_source_h__ */
diff --git a/libs/ardour/ardour/capturing_processor.h b/libs/ardour/ardour/capturing_processor.h
index fb8354a517..77a8dd1a0c 100644
--- a/libs/ardour/ardour/capturing_processor.h
+++ b/libs/ardour/ardour/capturing_processor.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_capturing_processor_h__
-#define __ardour_capturing_processor_h__
+#pragma once
 
 #include "ardour/fixed_delay.h"
 #include "ardour/processor.h"
@@ -56,4 +55,3 @@ private:
 
 } // namespace ARDOUR
 
-#endif // __ardour_capturing_processor_h__
diff --git a/libs/ardour/ardour/chan_count.h b/libs/ardour/ardour/chan_count.h
index a62d5dc70f..87d5fbf066 100644
--- a/libs/ardour/ardour/chan_count.h
+++ b/libs/ardour/ardour/chan_count.h
@@ -19,8 +19,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_chan_count_h__
-#define __ardour_chan_count_h__
+#pragma once
 
 #include <cassert>
 #include <ostream>
@@ -216,5 +215,4 @@ private:
 
 LIBARDOUR_API std::ostream& operator<<(std::ostream& o, const ARDOUR::ChanCount& c);
 
-#endif // __ardour_chan_count_h__
 
diff --git a/libs/ardour/ardour/chan_mapping.h b/libs/ardour/ardour/chan_mapping.h
index 21838a1221..7a17e48499 100644
--- a/libs/ardour/ardour/chan_mapping.h
+++ b/libs/ardour/ardour/chan_mapping.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_chan_mapping_h__
-#define __ardour_chan_mapping_h__
+#pragma once
 
 #include <map>
 #include <cassert>
@@ -140,5 +139,4 @@ private:
 
 std::ostream& operator<<(std::ostream& o, const ARDOUR::ChanMapping& m);
 
-#endif // __ardour_chan_mapping_h__
 
diff --git a/libs/ardour/ardour/click.h b/libs/ardour/ardour/click.h
index 3af2f16e34..b0aa8545fd 100644
--- a/libs/ardour/ardour/click.h
+++ b/libs/ardour/ardour/click.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_click_h__
-#define __ardour_click_h__
+#pragma once
 
 #include <list>
 
@@ -63,4 +62,3 @@ protected:
 
 }; /* namespace ARDOUR */
 
-#endif /*__ardour_click_h__ */
diff --git a/libs/ardour/ardour/comparable_shared_ptr.h b/libs/ardour/ardour/comparable_shared_ptr.h
index 526e449d21..e670225575 100644
--- a/libs/ardour/ardour/comparable_shared_ptr.h
+++ b/libs/ardour/ardour/comparable_shared_ptr.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_comparable_shared_ptr_h__
-#define __ardour_comparable_shared_ptr_h__
+#pragma once
 
 #include "ardour/libardour_visibility.h"
 
@@ -60,4 +59,3 @@ class /*LIBARDOUR_API*/ ComparableSharedPtr : public std::shared_ptr<T>
 
 } // namespace ARDOUR
 
-#endif // __ardour_comparable_shared_ptr_h__
diff --git a/libs/ardour/ardour/control_group.h b/libs/ardour/ardour/control_group.h
index b053ce063e..df74837809 100644
--- a/libs/ardour/ardour/control_group.h
+++ b/libs/ardour/ardour/control_group.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libardour_control_group_h__
-#define __libardour_control_group_h__
+#pragma once
 
 #include <map>
 #include <memory>
@@ -114,4 +113,3 @@ class LIBARDOUR_API GainControlGroup : public ControlGroup
 
 } /* namespace */
 
-#endif /* __libardour_control_group_h__ */
diff --git a/libs/ardour/ardour/control_group_member.h b/libs/ardour/ardour/control_group_member.h
index 4729278dec..ca7e013efb 100644
--- a/libs/ardour/ardour/control_group_member.h
+++ b/libs/ardour/ardour/control_group_member.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libardour_control_group_member_h__
-#define __libardour_control_group_member_h__
+#pragma once
 
 namespace ARDOUR {
 
@@ -39,4 +38,3 @@ class LIBARDOUR_API ControlGroupMember
 
 } /* namespace */
 
-#endif /* __libardour_control_group_member_h__ */
diff --git a/libs/ardour/ardour/coreaudiosource.h b/libs/ardour/ardour/coreaudiosource.h
index c75e226d98..2cc0dead0e 100644
--- a/libs/ardour/ardour/coreaudiosource.h
+++ b/libs/ardour/ardour/coreaudiosource.h
@@ -19,8 +19,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __coreaudio_source_h__
-#define __coreaudio_source_h__
+#pragma once
 
 #ifdef COREAUDIO105
 #include "CAAudioFile.h"
@@ -72,5 +71,4 @@ class LIBARDOUR_API CoreAudioSource : public AudioFileSource {
 
 }; /* namespace ARDOUR */
 
-#endif /* __coreaudio_source_h__ */
 
diff --git a/libs/ardour/ardour/cycle_timer.h b/libs/ardour/ardour/cycle_timer.h
index e9f20c3501..29cc76b768 100644
--- a/libs/ardour/ardour/cycle_timer.h
+++ b/libs/ardour/ardour/cycle_timer.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_cycle_timer_h__
-#define __ardour_cycle_timer_h__
+#pragma once
 
 #include <string>
 #include <iostream>
@@ -95,4 +94,3 @@ extern StoringTimer ST;
 #define PT_TIMING_CHECK(x)
 #endif
 
-#endif /* __ardour_cycle_timer_h__ */
diff --git a/libs/ardour/ardour/cycles.h b/libs/ardour/ardour/cycles.h
index 4d4920219e..4cfac2367a 100644
--- a/libs/ardour/ardour/cycles.h
+++ b/libs/ardour/ardour/cycles.h
@@ -20,8 +20,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_cycles_h__
-#define __ardour_cycles_h__
+#pragma once
 
 #include <stdint.h>
 
@@ -252,4 +251,3 @@ static inline cycles_t get_cycles(void)
 
 #endif
 
-#endif /* __ardour_cycles_h__ */
diff --git a/libs/ardour/ardour/data_type.h b/libs/ardour/ardour/data_type.h
index 5eae0dfbb3..54a8619d6f 100644
--- a/libs/ardour/ardour/data_type.h
+++ b/libs/ardour/ardour/data_type.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_data_type_h__
-#define __ardour_data_type_h__
+#pragma once
 
 #include <string>
 #include <stdint.h>
@@ -127,5 +126,4 @@ private:
 
 } // namespace ARDOUR
 
-#endif // __ardour_data_type_h__
 
diff --git a/libs/ardour/ardour/debug.h b/libs/ardour/ardour/debug.h
index 3e6f2661fa..0500f96f4f 100644
--- a/libs/ardour/ardour/debug.h
+++ b/libs/ardour/ardour/debug.h
@@ -20,8 +20,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_debug_h__
-#define __ardour_debug_h__
+#pragma once
 
 #include <stdint.h>
 
@@ -120,4 +119,3 @@ namespace PBD {
 	}
 }
 
-#endif /* __ardour_debug_h__ */
diff --git a/libs/ardour/ardour/delayline.h b/libs/ardour/ardour/delayline.h
index 8710b58e6d..2f23fff7a4 100644
--- a/libs/ardour/ardour/delayline.h
+++ b/libs/ardour/ardour/delayline.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_delayline_h__
-#define __ardour_delayline_h__
+#pragma once
 
 #include <memory>
 
@@ -81,4 +80,3 @@ private:
 
 } // namespace ARDOUR
 
-#endif // __ardour_meter_h__
diff --git a/libs/ardour/ardour/delivery.h b/libs/ardour/ardour/delivery.h
index 05db44f797..4e2efc997c 100644
--- a/libs/ardour/ardour/delivery.h
+++ b/libs/ardour/ardour/delivery.h
@@ -20,8 +20,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_delivery_h__
-#define __ardour_delivery_h__
+#pragma once
 
 #include <string>
 
@@ -166,5 +165,4 @@ private:
 
 } // namespace ARDOUR
 
-#endif // __ardour__h__
 
diff --git a/libs/ardour/ardour/directory_names.h b/libs/ardour/ardour/directory_names.h
index ea04a8db0b..f55fc47c45 100644
--- a/libs/ardour/ardour/directory_names.h
+++ b/libs/ardour/ardour/directory_names.h
@@ -20,8 +20,7 @@
  */
 
 
-#ifndef __ardour_directory_names_h__
-#define __ardour_directory_names_h__
+#pragma once
 
 #include "ardour/libardour_visibility.h"
 
@@ -57,4 +56,3 @@ namespace ARDOUR {
 
 };
 
-#endif
diff --git a/libs/ardour/ardour/disk_io.h b/libs/ardour/ardour/disk_io.h
index 6c3e4dc807..0a6604ac85 100644
--- a/libs/ardour/ardour/disk_io.h
+++ b/libs/ardour/ardour/disk_io.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_disk_io_h__
-#define __ardour_disk_io_h__
+#pragma once
 
 #include <vector>
 #include <string>
@@ -192,4 +191,3 @@ protected:
 
 } // namespace ARDOUR
 
-#endif /* __ardour_disk_io_h__ */
diff --git a/libs/ardour/ardour/disk_writer.h b/libs/ardour/ardour/disk_writer.h
index bef6d77966..71f930138d 100644
--- a/libs/ardour/ardour/disk_writer.h
+++ b/libs/ardour/ardour/disk_writer.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_disk_writer_h__
-#define __ardour_disk_writer_h__
+#pragma once
 
 #include <atomic>
 #include <list>
@@ -208,4 +207,3 @@ private:
 
 } // namespace
 
-#endif /* __ardour_disk_writer_h__ */
diff --git a/libs/ardour/ardour/ebur128_analysis.h b/libs/ardour/ardour/ebur128_analysis.h
index 23145d8b9f..98e3f10d79 100644
--- a/libs/ardour/ardour/ebur128_analysis.h
+++ b/libs/ardour/ardour/ebur128_analysis.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_ebur128_analysis_h__
-#define __ardour_ebur128_analysis_h__
+#pragma once
 
 #include "ardour/audioanalyser.h"
 #include "ardour/readable.h"
@@ -49,4 +48,3 @@ private:
 
 } /* namespace */
 
-#endif /* __ardour_audioanalyser_h__ */
diff --git a/libs/ardour/ardour/element_import_handler.h b/libs/ardour/ardour/element_import_handler.h
index 0aa26a7cb3..4ca8102069 100644
--- a/libs/ardour/ardour/element_import_handler.h
+++ b/libs/ardour/ardour/element_import_handler.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_element_import_handler_h__
-#define __ardour_element_import_handler_h__
+#pragma once
 
 #include <list>
 #include <memory>
@@ -109,4 +108,3 @@ class LIBARDOUR_API ElementImportHandler
 
 } // namespace ARDOUR
 
-#endif
diff --git a/libs/ardour/ardour/element_importer.h b/libs/ardour/ardour/element_importer.h
index 903152c6fa..2e0f0ff5a0 100644
--- a/libs/ardour/ardour/element_importer.h
+++ b/libs/ardour/ardour/element_importer.h
@@ -19,8 +19,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_element_importer_h__
-#define __ardour_element_importer_h__
+#pragma once
 
 #include <string>
 #include <utility>
@@ -132,4 +131,3 @@ class LIBARDOUR_API ElementImporter
 
 } // namespace ARDOUR
 
-#endif
diff --git a/libs/ardour/ardour/event_ring_buffer.h b/libs/ardour/ardour/event_ring_buffer.h
index 1d47cbbcbf..555a2b293d 100644
--- a/libs/ardour/ardour/event_ring_buffer.h
+++ b/libs/ardour/ardour/event_ring_buffer.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_event_ring_buffer_h__
-#define __ardour_event_ring_buffer_h__
+#pragma once
 
 #include <algorithm>
 #include <iostream>
@@ -132,4 +131,3 @@ EventRingBuffer<Time>::write(Time time, Evoral::EventType type, uint32_t size, c
 
 } // namespace ARDOUR
 
-#endif // __ardour_event_ring_buffer_h__
diff --git a/libs/ardour/ardour/event_type_map.h b/libs/ardour/ardour/event_type_map.h
index 8a902523c2..21d58b4ab4 100644
--- a/libs/ardour/ardour/event_type_map.h
+++ b/libs/ardour/ardour/event_type_map.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_event_type_map_h__
-#define __ardour_event_type_map_h__
+#pragma once
 
 #include <map>
 #include <string>
@@ -69,5 +68,4 @@ private:
 
 } // namespace ARDOUR
 
-#endif /* __ardour_event_type_map_h__ */
 
diff --git a/libs/ardour/ardour/export_analysis.h b/libs/ardour/ardour/export_analysis.h
index 53998174db..53a9a08579 100644
--- a/libs/ardour/ardour/export_analysis.h
+++ b/libs/ardour/ardour/export_analysis.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_export_analysis_h__
-#define __ardour_export_analysis_h__
+#pragma once
 
 #include <cstring>
 #include <map>
@@ -151,4 +150,3 @@ typedef std::shared_ptr<ExportAnalysis>        ExportAnalysisPtr;
 typedef std::map<std::string, ExportAnalysisPtr> AnalysisResults;
 
 } // namespace ARDOUR
-#endif
diff --git a/libs/ardour/ardour/export_channel.h b/libs/ardour/ardour/export_channel.h
index 9cc09499b3..e7188e72c8 100644
--- a/libs/ardour/ardour/export_channel.h
+++ b/libs/ardour/ardour/export_channel.h
@@ -20,8 +20,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_export_channel_h__
-#define __ardour_export_channel_h__
+#pragma once
 
 #include <list>
 #include <memory>
@@ -290,4 +289,3 @@ private:
 
 } // namespace ARDOUR
 
-#endif
diff --git a/libs/ardour/ardour/export_channel_configuration.h b/libs/ardour/ardour/export_channel_configuration.h
index 80d89c439d..3d0883b89e 100644
--- a/libs/ardour/ardour/export_channel_configuration.h
+++ b/libs/ardour/ardour/export_channel_configuration.h
@@ -19,8 +19,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_export_channel_configuration_h__
-#define __ardour_export_channel_configuration_h__
+#pragma once
 
 #include <algorithm>
 #include <list>
@@ -91,4 +90,3 @@ private:
 
 } // namespace ARDOUR
 
-#endif /* __ardour_export_channel_configuration_h__ */
diff --git a/libs/ardour/ardour/export_failed.h b/libs/ardour/ardour/export_failed.h
index f15547fc75..a408f2d7b9 100644
--- a/libs/ardour/ardour/export_failed.h
+++ b/libs/ardour/ardour/export_failed.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_export_failed_h__
-#define __ardour_export_failed_h__
+#pragma once
 
 #include <exception>
 #include <string>
@@ -48,4 +47,3 @@ class LIBARDOUR_API ExportFailed : public std::exception
 
 } // namespace ARDOUR
 
-#endif /* __ardour_export_failed_h__ */
diff --git a/libs/ardour/ardour/export_filename.h b/libs/ardour/ardour/export_filename.h
index ed75939e83..ca35e07bed 100644
--- a/libs/ardour/ardour/export_filename.h
+++ b/libs/ardour/ardour/export_filename.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_export_filename_h__
-#define __ardour_export_filename_h__
+#pragma once
 
 #include <memory>
 #include <string>
@@ -129,4 +128,3 @@ class LIBARDOUR_API ExportFilename {
 
 } // namespace ARDOUR
 
-#endif /* __ardour_export_filename_h__ */
diff --git a/libs/ardour/ardour/export_format_base.h b/libs/ardour/ardour/export_format_base.h
index 5b4a63ad3f..a9393f704d 100644
--- a/libs/ardour/ardour/export_format_base.h
+++ b/libs/ardour/ardour/export_format_base.h
@@ -19,8 +19,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_export_format_base_h__
-#define __ardour_export_format_base_h__
+#pragma once
 
 #include <memory>
 #include <set>
@@ -205,4 +204,3 @@ class LIBARDOUR_API ExportFormatBase {
 
 } // namespace ARDOUR
 
-#endif /* __ardour_export_format_base_h__ */
diff --git a/libs/ardour/ardour/export_format_compatibility.h b/libs/ardour/ardour/export_format_compatibility.h
index ba39ac4aa8..7c60d861f6 100644
--- a/libs/ardour/ardour/export_format_compatibility.h
+++ b/libs/ardour/ardour/export_format_compatibility.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_export_format_compatibility_h__
-#define __ardour_export_format_compatibility_h__
+#pragma once
 
 #include <string>
 #include "ardour/export_format_base.h"
@@ -54,4 +53,3 @@ class LIBARDOUR_API ExportFormatCompatibility : public ExportFormatBase, public
 
 } // namespace ARDOUR
 
-#endif /* __ardour_export_format_compatibility_h__ */
diff --git a/libs/ardour/ardour/export_format_manager.h b/libs/ardour/ardour/export_format_manager.h
index 50b7b4729b..341e0aea93 100644
--- a/libs/ardour/ardour/export_format_manager.h
+++ b/libs/ardour/ardour/export_format_manager.h
@@ -20,8 +20,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_export_format_manager_h__
-#define __ardour_export_format_manager_h__
+#pragma once
 
 #include <list>
 #include <memory>
@@ -181,4 +180,3 @@ class LIBARDOUR_API ExportFormatManager : public PBD::ScopedConnectionList
 
 } // namespace ARDOUR
 
-#endif /* __ardour_export_format_manager_h__ */
diff --git a/libs/ardour/ardour/export_format_specification.h b/libs/ardour/ardour/export_format_specification.h
index b32e6da2dc..fa7b819829 100644
--- a/libs/ardour/ardour/export_format_specification.h
+++ b/libs/ardour/ardour/export_format_specification.h
@@ -21,8 +21,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_export_format_specification_h__
-#define __ardour_export_format_specification_h__
+#pragma once
 
 #include <string>
 
@@ -265,4 +264,3 @@ class LIBARDOUR_API ExportFormatSpecification : public ExportFormatBase {
 
 } // namespace ARDOUR
 
-#endif /* __ardour_export_format_specification_h__ */
diff --git a/libs/ardour/ardour/export_formats.h b/libs/ardour/ardour/export_formats.h
index 97ab7850b7..dbed0ed089 100644
--- a/libs/ardour/ardour/export_formats.h
+++ b/libs/ardour/ardour/export_formats.h
@@ -19,8 +19,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_export_formats_h__
-#define __ardour_export_formats_h__
+#pragma once
 
 #include <list>
 #include <memory>
@@ -435,4 +434,3 @@ public:
 
 } // namespace ARDOUR
 
-#endif /* __ardour_export_formats__ */
diff --git a/libs/ardour/ardour/export_graph_builder.h b/libs/ardour/ardour/export_graph_builder.h
index e0b1654420..cedd019e4c 100644
--- a/libs/ardour/ardour/export_graph_builder.h
+++ b/libs/ardour/ardour/export_graph_builder.h
@@ -19,8 +19,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_export_graph_builder_h__
-#define __ardour_export_graph_builder_h__
+#pragma once
 
 #include "ardour/export_handler.h"
 #include "ardour/export_analysis.h"
@@ -322,4 +321,3 @@ class LIBARDOUR_API ExportGraphBuilder
 
 } // namespace ARDOUR
 
-#endif /* __ardour_export_graph_builder_h__ */
diff --git a/libs/ardour/ardour/export_handler.h b/libs/ardour/ardour/export_handler.h
index 97479540f6..a5806204d2 100644
--- a/libs/ardour/ardour/export_handler.h
+++ b/libs/ardour/ardour/export_handler.h
@@ -21,8 +21,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_export_handler_h__
-#define __ardour_export_handler_h__
+#pragma once
 
 #include <map>
 #include <memory>
@@ -237,4 +236,3 @@ class LIBARDOUR_API ExportHandler : public ExportElementFactory, public sigc::tr
 
 } // namespace ARDOUR
 
-#endif /* __ardour_export_handler_h__ */
diff --git a/libs/ardour/ardour/export_pointers.h b/libs/ardour/ardour/export_pointers.h
index 5e65ea603a..e1f224b5ee 100644
--- a/libs/ardour/ardour/export_pointers.h
+++ b/libs/ardour/ardour/export_pointers.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_export_pointers_h__
-#define __ardour_export_pointers_h__
+#pragma once
 
 #include <memory>
 
@@ -63,4 +62,3 @@ typedef std::shared_ptr<AudioGrapher::BroadcastInfo> BroadcastInfoPtr;
 
 } // namespace ARDOUR
 
-#endif // __ardour_export_pointers_h__
diff --git a/libs/ardour/ardour/export_preset.h b/libs/ardour/ardour/export_preset.h
index 130adfd893..fb88dc3b15 100644
--- a/libs/ardour/ardour/export_preset.h
+++ b/libs/ardour/ardour/export_preset.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_export_preset_h__
-#define __ardour_export_preset_h__
+#pragma once
 
 #include <string>
 
@@ -72,4 +71,3 @@ class LIBARDOUR_API ExportPreset {
 
 } // namespace ARDOUR
 
-#endif // __ardour_export_preset_h__
diff --git a/libs/ardour/ardour/export_profile_manager.h b/libs/ardour/ardour/export_profile_manager.h
index 6f0b95b3ef..41f21847a3 100644
--- a/libs/ardour/ardour/export_profile_manager.h
+++ b/libs/ardour/ardour/export_profile_manager.h
@@ -21,8 +21,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_export_profile_manager_h__
-#define __ardour_export_profile_manager_h__
+#pragma once
 
 #include <list>
 #include <map>
@@ -302,4 +301,3 @@ private:
 
 } // namespace ARDOUR
 
-#endif /* __ardour_export_profile_manager_h__ */
diff --git a/libs/ardour/ardour/export_status.h b/libs/ardour/ardour/export_status.h
index 7f36e60e06..b6370c9481 100644
--- a/libs/ardour/ardour/export_status.h
+++ b/libs/ardour/ardour/export_status.h
@@ -20,8 +20,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_export_status_h__
-#define __ardour_export_status_h__
+#pragma once
 
 #include <stdint.h>
 
@@ -95,4 +94,3 @@ class LIBARDOUR_API ExportStatus {
 
 } // namespace ARDOUR
 
-#endif /* __ardour_export_status_h__ */
diff --git a/libs/ardour/ardour/export_timespan.h b/libs/ardour/ardour/export_timespan.h
index 88eca8aa09..5bf1940310 100644
--- a/libs/ardour/ardour/export_timespan.h
+++ b/libs/ardour/ardour/export_timespan.h
@@ -20,8 +20,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_export_timespan_h__
-#define __ardour_export_timespan_h__
+#pragma once
 
 #include <memory>
 #include <string>
@@ -89,4 +88,3 @@ private:
 
 } // namespace ARDOUR
 
-#endif /* __ardour_export_timespan_h__ */
diff --git a/libs/ardour/ardour/file_source.h b/libs/ardour/ardour/file_source.h
index 84ef31f494..b6ec2edc6c 100644
--- a/libs/ardour/ardour/file_source.h
+++ b/libs/ardour/ardour/file_source.h
@@ -19,8 +19,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_filesource_h__
-#define __ardour_filesource_h__
+#pragma once
 
 #include <list>
 #include <string>
@@ -119,5 +118,4 @@ public:
 
 } // namespace ARDOUR
 
-#endif /* __ardour_filesource_h__ */
 
diff --git a/libs/ardour/ardour/filename_extensions.h b/libs/ardour/ardour/filename_extensions.h
index 1f750dae3e..4390527df6 100644
--- a/libs/ardour/ardour/filename_extensions.h
+++ b/libs/ardour/ardour/filename_extensions.h
@@ -19,8 +19,7 @@
  */
 
 
-#ifndef __ardour_filename_extensions_h__
-#define __ardour_filename_extensions_h__
+#pragma once
 
 #include "ardour/libardour_visibility.h"
 
@@ -41,4 +40,3 @@ namespace ARDOUR {
 	LIBARDOUR_API extern const char* const advanced_authoring_format_suffix;
 }
 
-#endif
diff --git a/libs/ardour/ardour/filter.h b/libs/ardour/ardour/filter.h
index f4fbcabf33..07d9b57188 100644
--- a/libs/ardour/ardour/filter.h
+++ b/libs/ardour/ardour/filter.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_filter_h__
-#define __ardour_filter_h__
+#pragma once
 
 #include <vector>
 
@@ -53,4 +52,3 @@ class LIBARDOUR_API Filter {
 
 } /* namespace */
 
-#endif /* __ardour_filter_h__ */
diff --git a/libs/ardour/ardour/fixed_delay.h b/libs/ardour/ardour/fixed_delay.h
index 90bfcebf59..fe1f6e906e 100644
--- a/libs/ardour/ardour/fixed_delay.h
+++ b/libs/ardour/ardour/fixed_delay.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_fixed_delay_h__
-#define __ardour_fixed_delay_h__
+#pragma once
 
 #include <vector>
 #include "ardour/buffer.h"
@@ -112,4 +111,3 @@ private:
 
 } // namespace ARDOUR
 
-#endif // __ardour_fixed_delay_h__
diff --git a/libs/ardour/ardour/gain_control.h b/libs/ardour/ardour/gain_control.h
index 491705bafe..a5e203f8b8 100644
--- a/libs/ardour/ardour/gain_control.h
+++ b/libs/ardour/ardour/gain_control.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_gain_control_h__
-#define __ardour_gain_control_h__
+#pragma once
 
 #include <memory>
 #include <string>
@@ -49,4 +48,3 @@ protected:
 
 } /* namespace */
 
-#endif /* __ardour_gain_control_h__ */
diff --git a/libs/ardour/ardour/graph.h b/libs/ardour/ardour/graph.h
index 718df6da39..b36fb1e94a 100644
--- a/libs/ardour/ardour/graph.h
+++ b/libs/ardour/ardour/graph.h
@@ -20,8 +20,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_graph_h__
-#define __ardour_graph_h__
+#pragma once
 
 #include <atomic>
 #include <list>
@@ -153,4 +152,3 @@ private:
 
 } // namespace ARDOUR
 
-#endif /* __ardour_graph_h__ */
diff --git a/libs/ardour/ardour/graph_edges.h b/libs/ardour/ardour/graph_edges.h
index 98faf2ace0..6a69c821fd 100644
--- a/libs/ardour/ardour/graph_edges.h
+++ b/libs/ardour/ardour/graph_edges.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_route_graph_h__
-#define __ardour_route_graph_h__
+#pragma once
 
 #include <map>
 #include <set>
@@ -82,4 +81,3 @@ bool topological_sort (GraphNodeList&, GraphEdges&);
 
 }
 
-#endif
diff --git a/libs/ardour/ardour/graphnode.h b/libs/ardour/ardour/graphnode.h
index 1675597540..3dfacc77c7 100644
--- a/libs/ardour/ardour/graphnode.h
+++ b/libs/ardour/ardour/graphnode.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_graphnode_h__
-#define __ardour_graphnode_h__
+#pragma once
 
 #include <atomic>
 #include <list>
@@ -100,4 +99,3 @@ private:
 
 } // namespace ARDOUR
 
-#endif
diff --git a/libs/ardour/ardour/import_status.h b/libs/ardour/ardour/import_status.h
index 713fca5850..62c3bf9ff7 100644
--- a/libs/ardour/ardour/import_status.h
+++ b/libs/ardour/ardour/import_status.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_import_status_h__
-#define __ardour_import_status_h__
+#pragma once
 
 #include <string>
 #include <vector>
@@ -67,4 +66,3 @@ public:
 
 } // namespace ARDOUR
 
-#endif /* __ardour_import_status_h__ */
diff --git a/libs/ardour/ardour/importable_source.h b/libs/ardour/ardour/importable_source.h
index 4147fd46d4..bcab3fb347 100644
--- a/libs/ardour/ardour/importable_source.h
+++ b/libs/ardour/ardour/importable_source.h
@@ -19,8 +19,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_importable_source_h__
-#define __ardour_importable_source_h__
+#pragma once
 
 #include "pbd/failed_constructor.h"
 #include "ardour/libardour_visibility.h"
@@ -46,4 +45,3 @@ public:
 
 }
 
-#endif /* __ardour_importable_source_h__ */
diff --git a/libs/ardour/ardour/instrument_info.h b/libs/ardour/ardour/instrument_info.h
index 9207b98cb6..23080093f4 100644
--- a/libs/ardour/ardour/instrument_info.h
+++ b/libs/ardour/ardour/instrument_info.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_instrument_info_h__
-#define __ardour_instrument_info_h__
+#pragma once
 
 #include <memory>
 #include <stdint.h>
@@ -101,4 +100,3 @@ private:
 
 }
 
-#endif /* __ardour_instrument_info_h__ */
diff --git a/libs/ardour/ardour/internal_return.h b/libs/ardour/ardour/internal_return.h
index 51655c9d6a..9c2d359338 100644
--- a/libs/ardour/ardour/internal_return.h
+++ b/libs/ardour/ardour/internal_return.h
@@ -19,8 +19,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_internal_return_h__
-#define __ardour_internal_return_h__
+#pragma once
 
 #include <list>
 
@@ -57,4 +56,3 @@ private:
 
 } // namespace ARDOUR
 
-#endif /* __ardour_internal_return_h__ */
diff --git a/libs/ardour/ardour/internal_send.h b/libs/ardour/ardour/internal_send.h
index aa26cc2518..cd5118f01a 100644
--- a/libs/ardour/ardour/internal_send.h
+++ b/libs/ardour/ardour/internal_send.h
@@ -20,8 +20,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_internal_send_h__
-#define __ardour_internal_send_h__
+#pragma once
 
 #include "ardour/ardour.h"
 #include "ardour/send.h"
@@ -90,4 +89,3 @@ private:
 
 } // namespace ARDOUR
 
-#endif /* __ardour_send_h__ */
diff --git a/libs/ardour/ardour/interthread_info.h b/libs/ardour/ardour/interthread_info.h
index 92b78116cb..9a2af3ac0e 100644
--- a/libs/ardour/ardour/interthread_info.h
+++ b/libs/ardour/ardour/interthread_info.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libardour_interthread_h__
-#define __libardour_interthread_h__
+#pragma once
 
 #include <pthread.h>
 
@@ -40,4 +39,3 @@ namespace ARDOUR {
 
 } // namespace
 
-#endif /* __libardour_interthread_h__ */
diff --git a/libs/ardour/ardour/io.h b/libs/ardour/ardour/io.h
index e4cef915ab..88e84178cf 100644
--- a/libs/ardour/ardour/io.h
+++ b/libs/ardour/ardour/io.h
@@ -20,8 +20,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_io_h__
-#define __ardour_io_h__
+#pragma once
 
 #include <string>
 #include <vector>
@@ -255,4 +254,3 @@ namespace PBD {
 	DEFINE_ENUM_CONVERT (ARDOUR::IO::Direction)
 }
 
-#endif /*__ardour_io_h__ */
diff --git a/libs/ardour/ardour/io_processor.h b/libs/ardour/ardour/io_processor.h
index 15ffad7d72..c181f6d266 100644
--- a/libs/ardour/ardour/io_processor.h
+++ b/libs/ardour/ardour/io_processor.h
@@ -19,8 +19,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_redirect_h__
-#define __ardour_redirect_h__
+#pragma once
 
 #include <memory>
 #include <string>
@@ -104,4 +103,3 @@ private:
 
 } // namespace ARDOUR
 
-#endif /* __ardour_redirect_h__ */
diff --git a/libs/ardour/ardour/io_vector.h b/libs/ardour/ardour/io_vector.h
index 54e2f64175..1bec2e889c 100644
--- a/libs/ardour/ardour/io_vector.h
+++ b/libs/ardour/ardour/io_vector.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_io_vector_h__
-#define __ardour_io_vector_h__
+#pragma once
 
 #include <memory>
 #include <vector>
@@ -68,4 +67,3 @@ public:
 } // namespace ARDOUR
 
 
-#endif
diff --git a/libs/ardour/ardour/ladspa_plugin.h b/libs/ardour/ardour/ladspa_plugin.h
index fe64a09673..ec8ec54cca 100644
--- a/libs/ardour/ardour/ladspa_plugin.h
+++ b/libs/ardour/ardour/ladspa_plugin.h
@@ -20,8 +20,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_ladspa_plugin_h__
-#define __ardour_ladspa_plugin_h__
+#pragma once
 
 #include <set>
 #include <vector>
@@ -167,4 +166,3 @@ typedef std::shared_ptr<LadspaPluginInfo> LadspaPluginInfoPtr;
 
 } // namespace ARDOUR
 
-#endif /* __ardour_ladspa_plugin_h__ */
diff --git a/libs/ardour/ardour/latent.h b/libs/ardour/ardour/latent.h
index 0e34d3c81a..a06b1392a7 100644
--- a/libs/ardour/ardour/latent.h
+++ b/libs/ardour/ardour/latent.h
@@ -19,8 +19,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_latent_h__
-#define __ardour_latent_h__
+#pragma once
 
 #include "pbd/signals.h"
 
@@ -101,4 +100,3 @@ private:
 } /* namespace */
 
 
-#endif /* __ardour_latent_h__*/
diff --git a/libs/ardour/ardour/legatize.h b/libs/ardour/ardour/legatize.h
index 9aca0ab5e5..e0a02c51b5 100644
--- a/libs/ardour/ardour/legatize.h
+++ b/libs/ardour/ardour/legatize.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_legatize_h__
-#define __ardour_legatize_h__
+#pragma once
 
 #include <string>
 
@@ -53,4 +52,3 @@ private:
 
 } /* namespace */
 
-#endif /* __ardour_legatize_h__ */
diff --git a/libs/ardour/ardour/libardour_visibility.h b/libs/ardour/ardour/libardour_visibility.h
index 3f1482e300..e8ef02f7c1 100644
--- a/libs/ardour/ardour/libardour_visibility.h
+++ b/libs/ardour/ardour/libardour_visibility.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libardour_libardour_visibility_h__
-#define __libardour_libardour_visibility_h__
+#pragma once
 
 #if defined(COMPILER_MSVC)
   #define LIBARDOUR_DLL_IMPORT __declspec(dllimport)
@@ -41,4 +40,3 @@
   #define LIBARDOUR_LOCAL LIBARDOUR_DLL_LOCAL
 #endif
 
-#endif /* __libardour_libardour_visibility_h__ */
diff --git a/libs/ardour/ardour/library.h b/libs/ardour/ardour/library.h
index 8ada7a4b02..cfd7c26839 100644
--- a/libs/ardour/ardour/library.h
+++ b/libs/ardour/ardour/library.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libardour_library_h__
-#define __libardour_library_h__
+#pragma once
 
 #include <cstdio>
 #include <cstdint>
@@ -79,4 +78,3 @@ class LIBARDOUR_API LibraryFetcher {
 
 } /* namespace */
 
-#endif
diff --git a/libs/ardour/ardour/linux_vst_support.h b/libs/ardour/ardour/linux_vst_support.h
index 2302198e13..5af833ef18 100644
--- a/libs/ardour/ardour/linux_vst_support.h
+++ b/libs/ardour/ardour/linux_vst_support.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __vstfx_h__
-#define __vstfx_h__
+#pragma once
 
 #include <setjmp.h>
 #include <signal.h>
@@ -52,4 +51,3 @@ LIBARDOUR_API extern void         vstfx_destroy_editor (VSTState *);
 
 LIBARDOUR_API extern void         vstfx_event_loop_remove_plugin (VSTState *);
 
-#endif /* __vstfx_h__ */
diff --git a/libs/ardour/ardour/location.h b/libs/ardour/ardour/location.h
index 54b2e787d8..38047fc487 100644
--- a/libs/ardour/ardour/location.h
+++ b/libs/ardour/ardour/location.h
@@ -22,8 +22,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_location_h__
-#define __ardour_location_h__
+#pragma once
 
 #include <string>
 #include <list>
@@ -371,4 +370,3 @@ private:
 
 } // namespace ARDOUR
 
-#endif /* __ardour_location_h__ */
diff --git a/libs/ardour/ardour/location_importer.h b/libs/ardour/ardour/location_importer.h
index 5b468d60e7..270a1164d8 100644
--- a/libs/ardour/ardour/location_importer.h
+++ b/libs/ardour/ardour/location_importer.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_location_importer_h__
-#define __ardour_location_importer_h__
+#pragma once
 
 #include <memory>
 
@@ -62,4 +61,3 @@ class LIBARDOUR_API LocationImporter : public ElementImporter
 
 } // namespace ARDOUR
 
-#endif
diff --git a/libs/ardour/ardour/logcurve.h b/libs/ardour/ardour/logcurve.h
index 0f040fc8ca..bfab98533f 100644
--- a/libs/ardour/ardour/logcurve.h
+++ b/libs/ardour/ardour/logcurve.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_logcurve_h__
-#define __ardour_logcurve_h__
+#pragma once
 
 #include "pbd/fastlog.h"
 #include <glibmm/threads.h>
@@ -128,6 +127,5 @@ class LIBARDOUR_API LogCurveOut : public LogCurve
 
 } // namespace ARDOUR
 
-#endif /* __ardour_logcurve_h__ */
 
 
diff --git a/libs/ardour/ardour/logmeter.h b/libs/ardour/ardour/logmeter.h
index 8b4716afb4..82ab6d23ae 100644
--- a/libs/ardour/ardour/logmeter.h
+++ b/libs/ardour/ardour/logmeter.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_gtk_log_meter_h__
-#define __ardour_gtk_log_meter_h__
+#pragma once
 
 #include "ardour/dB.h"
 
@@ -168,4 +167,3 @@ meter_deflect_k (float db, float krange)
 	}
 }
 
-#endif /* __ardour_gtk_log_meter_h__ */
diff --git a/libs/ardour/ardour/ltc_file_reader.h b/libs/ardour/ardour/ltc_file_reader.h
index 3b72014e2d..e21549bac6 100644
--- a/libs/ardour/ardour/ltc_file_reader.h
+++ b/libs/ardour/ardour/ltc_file_reader.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libardour_ltc_file_reader_h__
-#define __libardour_ltc_file_reader_h__
+#pragma once
 
 #include <vector>
 #include <sndfile.h>
@@ -85,4 +84,3 @@ private:
 
 } // namespace ARDOUR
 
-#endif /* __libardour_ltc_file_reader_h__ */
diff --git a/libs/ardour/ardour/luabindings.h b/libs/ardour/ardour/luabindings.h
index 9b1513e9e1..ac2b25b75f 100644
--- a/libs/ardour/ardour/luabindings.h
+++ b/libs/ardour/ardour/luabindings.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_luabindings_h__
-#define __ardour_luabindings_h__
+#pragma once
 
 #include "lua/lua.h"
 #include "ardour/libardour_visibility.h"
@@ -37,4 +36,3 @@ namespace ARDOUR {
 	} // namespace LuaBindings
 } // namespace ARDOUR
 
-#endif /* __ardour_luabindings_h__ */
diff --git a/libs/ardour/ardour/luaproc.h b/libs/ardour/ardour/luaproc.h
index 06478503f5..b1e6c6da2f 100644
--- a/libs/ardour/ardour/luaproc.h
+++ b/libs/ardour/ardour/luaproc.h
@@ -23,8 +23,7 @@
 //#define USE_TLSF // use TLSF instead of ReallocPool
 //#define USE_MALLOC // or plain OS provided realloc (no mlock) -- if USE_TLSF isn't defined
 
-#ifndef __ardour_luaproc_h__
-#define __ardour_luaproc_h__
+#pragma once
 
 #include <set>
 #include <vector>
@@ -246,4 +245,3 @@ typedef std::shared_ptr<LuaPluginInfo> LuaPluginInfoPtr;
 
 } // namespace ARDOUR
 
-#endif // __ardour_luaproc_h__
diff --git a/libs/ardour/ardour/lxvst_plugin.h b/libs/ardour/ardour/lxvst_plugin.h
index 7b6492da6b..3ef3281d93 100644
--- a/libs/ardour/ardour/lxvst_plugin.h
+++ b/libs/ardour/ardour/lxvst_plugin.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_lxvst_plugin_h__
-#define __ardour_lxvst_plugin_h__
+#pragma once
 
 #include "ardour/vst_plugin.h"
 
@@ -51,4 +50,3 @@ class LIBARDOUR_API LXVSTPluginInfo : public VSTPluginInfo
 
 } // namespace ARDOUR
 
-#endif /* __ardour_lxvst_plugin_h__ */
diff --git a/libs/ardour/ardour/mac_vst_plugin.h b/libs/ardour/ardour/mac_vst_plugin.h
index 98ca8d1946..8d2235237e 100644
--- a/libs/ardour/ardour/mac_vst_plugin.h
+++ b/libs/ardour/ardour/mac_vst_plugin.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_mac_vst_plugin_h__
-#define __ardour_mac_vst_plugin_h__
+#pragma once
 
 #include "ardour/vst_plugin.h"
 
@@ -54,4 +53,3 @@ public:
 
 } // namespace ARDOUR
 
-#endif /* __ardour_mac_vst_plugin_h__ */
diff --git a/libs/ardour/ardour/mac_vst_support.h b/libs/ardour/ardour/mac_vst_support.h
index c2b6146219..9116ddf3f9 100644
--- a/libs/ardour/ardour/mac_vst_support.h
+++ b/libs/ardour/ardour/mac_vst_support.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __mac_vst_support_h__
-#define __mac_vst_support_h__
+#pragma once
 
 #include <setjmp.h>
 #include <signal.h>
@@ -35,4 +34,3 @@ LIBARDOUR_API extern int          mac_vst_unload (VSTHandle *);
 LIBARDOUR_API extern VSTState *   mac_vst_instantiate (VSTHandle *, audioMasterCallback, void *);
 LIBARDOUR_API extern void         mac_vst_close (VSTState*);
 
-#endif /* ____mac_vst_support_h__ */
diff --git a/libs/ardour/ardour/meter.h b/libs/ardour/ardour/meter.h
index e031d3da47..1861ed9b7f 100644
--- a/libs/ardour/ardour/meter.h
+++ b/libs/ardour/ardour/meter.h
@@ -19,8 +19,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_meter_h__
-#define __ardour_meter_h__
+#pragma once
 
 #include <atomic>
 #include <vector>
@@ -119,4 +118,3 @@ private:
 
 } // namespace ARDOUR
 
-#endif // __ardour_meter_h__
diff --git a/libs/ardour/ardour/midi_automation_list_binder.h b/libs/ardour/ardour/midi_automation_list_binder.h
index fb4b28ea60..554845d1a8 100644
--- a/libs/ardour/ardour/midi_automation_list_binder.h
+++ b/libs/ardour/ardour/midi_automation_list_binder.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_midi_automation_list_binder_h__
-#define __ardour_midi_automation_list_binder_h__
+#pragma once
 
 #include "pbd/memento_command.h"
 #include "evoral/Parameter.h"
@@ -55,4 +54,3 @@ private:
 
 } // namespace ARDOUR
 
-#endif // __ardour_midi_automation_list_binder_h__
diff --git a/libs/ardour/ardour/midi_buffer.h b/libs/ardour/ardour/midi_buffer.h
index a6b0e8e63b..8602e1a5de 100644
--- a/libs/ardour/ardour/midi_buffer.h
+++ b/libs/ardour/ardour/midi_buffer.h
@@ -20,8 +20,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_midi_buffer_h__
-#define __ardour_midi_buffer_h__
+#pragma once
 
 #include "evoral/Event.h"
 #include "evoral/EventSink.h"
@@ -217,4 +216,3 @@ private:
 
 } // namespace ARDOUR
 
-#endif // __ardour_midi_buffer_h__
diff --git a/libs/ardour/ardour/midi_channel_filter.h b/libs/ardour/ardour/midi_channel_filter.h
index 59f83402da..83b92f956d 100644
--- a/libs/ardour/ardour/midi_channel_filter.h
+++ b/libs/ardour/ardour/midi_channel_filter.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_channel_filter_h__
-#define __ardour_channel_filter_h__
+#pragma once
 
 #include <atomic>
 #include <cstdint>
@@ -95,4 +94,3 @@ private:
 
 } /* namespace ARDOUR */
 
-#endif /* __ardour_channel_filter_h__ */
diff --git a/libs/ardour/ardour/midi_cursor.h b/libs/ardour/ardour/midi_cursor.h
index 1fdd60b729..c40a2f4b35 100644
--- a/libs/ardour/ardour/midi_cursor.h
+++ b/libs/ardour/ardour/midi_cursor.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_midi_cursor_h__
-#define __ardour_midi_cursor_h__
+#pragma once
 
 #include <set>
 
@@ -55,4 +54,3 @@ struct MidiCursor : public boost::noncopyable {
 
 }
 
-#endif /* __ardour_midi_cursor_h__ */
diff --git a/libs/ardour/ardour/midi_model.h b/libs/ardour/ardour/midi_model.h
index fc08e5a27a..18fd4da7b8 100644
--- a/libs/ardour/ardour/midi_model.h
+++ b/libs/ardour/ardour/midi_model.h
@@ -21,8 +21,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_midi_model_h__
-#define __ardour_midi_model_h__
+#pragma once
 
 #include <deque>
 #include <map>
@@ -379,5 +378,4 @@ private:
 
 } /* namespace ARDOUR */
 
-#endif /* __ardour_midi_model_h__ */
 
diff --git a/libs/ardour/ardour/midi_operator.h b/libs/ardour/ardour/midi_operator.h
index 214db360d8..7a79467365 100644
--- a/libs/ardour/ardour/midi_operator.h
+++ b/libs/ardour/ardour/midi_operator.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libardour_midi_operator_h__
-#define __libardour_midi_operator_h__
+#pragma once
 
 #include <vector>
 #include <string>
@@ -49,4 +48,3 @@ class LIBARDOUR_API MidiOperator {
 
 } /* namespace */
 
-#endif /* __libardour_midi_operator_h__ */
diff --git a/libs/ardour/ardour/midi_playlist.h b/libs/ardour/ardour/midi_playlist.h
index 4277cb5049..1da9061a0e 100644
--- a/libs/ardour/ardour/midi_playlist.h
+++ b/libs/ardour/ardour/midi_playlist.h
@@ -20,8 +20,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_midi_playlist_h__
-#define __ardour_midi_playlist_h__
+#pragma once
 
 #include <vector>
 #include <list>
@@ -95,4 +94,3 @@ public:
 
 } /* namespace ARDOUR */
 
-#endif /* __ardour_midi_playlist_h__ */
diff --git a/libs/ardour/ardour/midi_port.h b/libs/ardour/ardour/midi_port.h
index 3759a22cae..b52a8c4d61 100644
--- a/libs/ardour/ardour/midi_port.h
+++ b/libs/ardour/ardour/midi_port.h
@@ -19,8 +19,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_midi_port_h__
-#define __ardour_midi_port_h__
+#pragma once
 
 #include "midi++/parser.h"
 
@@ -91,4 +90,3 @@ private:
 
 } // namespace ARDOUR
 
-#endif /* __ardour_midi_port_h__ */
diff --git a/libs/ardour/ardour/midi_region.h b/libs/ardour/ardour/midi_region.h
index 220e0618aa..8d456e9c75 100644
--- a/libs/ardour/ardour/midi_region.h
+++ b/libs/ardour/ardour/midi_region.h
@@ -20,8 +20,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_midi_region_h__
-#define __ardour_midi_region_h__
+#pragma once
 
 #include <vector>
 
@@ -166,4 +165,3 @@ class LIBARDOUR_API MidiRegion : public Region
 } /* namespace ARDOUR */
 
 
-#endif /* __ardour_midi_region_h__ */
diff --git a/libs/ardour/ardour/midi_ring_buffer.h b/libs/ardour/ardour/midi_ring_buffer.h
index 3095e028ad..cdae4ff856 100644
--- a/libs/ardour/ardour/midi_ring_buffer.h
+++ b/libs/ardour/ardour/midi_ring_buffer.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_midi_ring_buffer_h__
-#define __ardour_midi_ring_buffer_h__
+#pragma once
 
 #include <iostream>
 #include <algorithm>
@@ -100,5 +99,4 @@ MidiRingBuffer<T>::read_contents(uint32_t size, uint8_t* buf)
 
 } // namespace ARDOUR
 
-#endif // __ardour_midi_ring_buffer_h__
 
diff --git a/libs/ardour/ardour/midi_scene_change.h b/libs/ardour/ardour/midi_scene_change.h
index 872a186181..c41c595f81 100644
--- a/libs/ardour/ardour/midi_scene_change.h
+++ b/libs/ardour/ardour/midi_scene_change.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libardour_midi_scene_change_h__
-#define __libardour_midi_scene_change_h__
+#pragma once
 
 #include "evoral/PatchChange.h"
 
@@ -63,4 +62,3 @@ class MIDISceneChange : public SceneChange
 } /* namespace */
 
 
-#endif /* __libardour_scene_change_h__ */
diff --git a/libs/ardour/ardour/midi_scene_changer.h b/libs/ardour/ardour/midi_scene_changer.h
index ce30ce1f9e..b1c4bf6824 100644
--- a/libs/ardour/ardour/midi_scene_changer.h
+++ b/libs/ardour/ardour/midi_scene_changer.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libardour_midi_scene_changer_h__
-#define __libardour_midi_scene_changer_h__
+#pragma once
 
 #include <glibmm/threads.h>
 
@@ -82,4 +81,3 @@ class MIDISceneChanger : public SceneChanger
 
 } // namespace
 
-#endif /* __libardour_midi_scene_changer_h__ */
diff --git a/libs/ardour/ardour/midi_source.h b/libs/ardour/ardour/midi_source.h
index e28ef43e5e..42205bfd11 100644
--- a/libs/ardour/ardour/midi_source.h
+++ b/libs/ardour/ardour/midi_source.h
@@ -20,8 +20,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_midi_source_h__
-#define __ardour_midi_source_h__
+#pragma once
 
 #include <string>
 #include <time.h>
@@ -248,4 +247,3 @@ class LIBARDOUR_API MidiSource : virtual public Source
 
 }
 
-#endif /* __ardour_midi_source_h__ */
diff --git a/libs/ardour/ardour/midi_state_tracker.h b/libs/ardour/ardour/midi_state_tracker.h
index 650d1c122a..db5b29ea8a 100644
--- a/libs/ardour/ardour/midi_state_tracker.h
+++ b/libs/ardour/ardour/midi_state_tracker.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_midi_state_tracker_h__
-#define __ardour_midi_state_tracker_h__
+#pragma once
 
 #include <glibmm/threads.h>
 
@@ -100,4 +99,3 @@ class LIBARDOUR_API MidiStateTracker : public MidiNoteTracker
 
 } // namespace ARDOUR
 
-#endif // __ardour_midi_state_tracker_h__
diff --git a/libs/ardour/ardour/midi_stretch.h b/libs/ardour/ardour/midi_stretch.h
index 11cbb283a2..964919f5be 100644
--- a/libs/ardour/ardour/midi_stretch.h
+++ b/libs/ardour/ardour/midi_stretch.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_midi_stretch_h__
-#define __ardour_midi_stretch_h__
+#pragma once
 
 #include "ardour/filter.h"
 #include "ardour/timefx_request.h"
@@ -38,4 +37,3 @@ class LIBARDOUR_API MidiStretch : public Filter {
 
 } /* namespace ARDOUR */
 
-#endif /* __ardour_midi_stretch_h__ */
diff --git a/libs/ardour/ardour/midi_track.h b/libs/ardour/ardour/midi_track.h
index a257608366..d46a7aec10 100644
--- a/libs/ardour/ardour/midi_track.h
+++ b/libs/ardour/ardour/midi_track.h
@@ -19,8 +19,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_midi_track_h__
-#define __ardour_midi_track_h__
+#pragma once
 
 #include "ardour/midi_channel_filter.h"
 #include "ardour/midi_ring_buffer.h"
@@ -190,4 +189,3 @@ private:
 
 } /* namespace ARDOUR*/
 
-#endif /* __ardour_midi_track_h__ */
diff --git a/libs/ardour/ardour/midi_ui.h b/libs/ardour/ardour/midi_ui.h
index 7b19277e83..2d0885aa8e 100644
--- a/libs/ardour/ardour/midi_ui.h
+++ b/libs/ardour/ardour/midi_ui.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libardour_midi_ui_h__
-#define __libardour_midi_ui_h__
+#pragma once
 
 #include <list>
 
@@ -69,4 +68,3 @@ class LIBARDOUR_API MidiControlUI : public AbstractUI<MidiUIRequest>
 
 }
 
-#endif /* __libardour_midi_ui_h__ */
diff --git a/libs/ardour/ardour/mididm.h b/libs/ardour/ardour/mididm.h
index 750c3bdeaa..eb4e585fc6 100644
--- a/libs/ardour/ardour/mididm.h
+++ b/libs/ardour/ardour/mididm.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libardour_mididm_h__
-#define __libardour_mididm_h__
+#pragma once
 
 #include "ardour/types.h"
 #include "ardour/libardour_visibility.h"
@@ -61,4 +60,3 @@ private:
 
 }
 
-#endif /* __libardour_mididm_h__ */
diff --git a/libs/ardour/ardour/midiport_manager.h b/libs/ardour/ardour/midiport_manager.h
index 0b433522df..0e174ef303 100644
--- a/libs/ardour/ardour/midiport_manager.h
+++ b/libs/ardour/ardour/midiport_manager.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __midiport_manager_h__
-#define __midiport_manager_h__
+#pragma once
 
 #include <list>
 
@@ -117,4 +116,3 @@ protected:
 
 } // namespace ARDOUR
 
-#endif
diff --git a/libs/ardour/ardour/mix.h b/libs/ardour/ardour/mix.h
index a77ebe0267..407eddf3a5 100644
--- a/libs/ardour/ardour/mix.h
+++ b/libs/ardour/ardour/mix.h
@@ -16,8 +16,7 @@
  * with this program; if not, write to the Free Software Foundation, Inc.,
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
-#ifndef __ardour_mix_h__
-#define __ardour_mix_h__
+#pragma once
 
 #include "ardour/libardour_visibility.h"
 #include "ardour/types.h"
@@ -106,4 +105,3 @@ LIBARDOUR_API void  default_mix_buffers_with_gain     (ARDOUR::Sample* dst, ARDO
 LIBARDOUR_API void  default_mix_buffers_no_gain       (ARDOUR::Sample* dst, ARDOUR::Sample const* src, ARDOUR::pframes_t nframes);
 LIBARDOUR_API void  default_copy_vector               (ARDOUR::Sample* dst, ARDOUR::Sample const* src, ARDOUR::pframes_t nframes);
 
-#endif /* __ardour_mix_h__ */
diff --git a/libs/ardour/ardour/mode.h b/libs/ardour/ardour/mode.h
index 1f0955b20e..40517b46b4 100644
--- a/libs/ardour/ardour/mode.h
+++ b/libs/ardour/ardour/mode.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_mode_h__
-#define __ardour_mode_h__
+#pragma once
 
 #include <vector>
 
@@ -73,4 +72,3 @@ class MusicalMode
 	static void fill (MusicalMode&, Type);
 };
 
-#endif /* __ardour_mode_h__ */
diff --git a/libs/ardour/ardour/monitor_control.h b/libs/ardour/ardour/monitor_control.h
index 151bcc2225..110ad10b47 100644
--- a/libs/ardour/ardour/monitor_control.h
+++ b/libs/ardour/ardour/monitor_control.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_monitor_control_h__
-#define __ardour_monitor_control_h__
+#pragma once
 
 #include <memory>
 #include <string>
@@ -53,4 +52,3 @@ class LIBARDOUR_API MonitorControl : public SlavableAutomationControl
 
 } /* namespace */
 
-#endif /* __libardour_monitor_control_h__ */
diff --git a/libs/ardour/ardour/monitor_processor.h b/libs/ardour/ardour/monitor_processor.h
index e58e8f0a5d..163455905b 100644
--- a/libs/ardour/ardour/monitor_processor.h
+++ b/libs/ardour/ardour/monitor_processor.h
@@ -20,8 +20,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_monitor_processor_h__
-#define __ardour_monitor_processor_h__
+#pragma once
 
 #include <algorithm>
 #include <iostream>
@@ -236,4 +235,3 @@ private:
 
 } /* namespace */
 
-#endif /* __ardour_monitor_processor_h__ */
diff --git a/libs/ardour/ardour/monitor_return.h b/libs/ardour/ardour/monitor_return.h
index 0d08cc41f7..483d02739f 100644
--- a/libs/ardour/ardour/monitor_return.h
+++ b/libs/ardour/ardour/monitor_return.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_monitor_return_h__
-#define __ardour_monitor_return_h__
+#pragma once
 
 #include "ardour/internal_return.h"
 
@@ -42,4 +41,3 @@ protected:
 
 } // namespace ARDOUR
 
-#endif
diff --git a/libs/ardour/ardour/monitorable.h b/libs/ardour/ardour/monitorable.h
index 2567d49a5c..57d7be5fec 100644
--- a/libs/ardour/ardour/monitorable.h
+++ b/libs/ardour/ardour/monitorable.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_monitorable_h__
-#define __ardour_monitorable_h__
+#pragma once
 
 #include "ardour/types.h"
 
@@ -32,4 +31,3 @@ class Monitorable {
 
 } /* namespace */
 
-#endif /* __ardour_monitorable_h__ */
diff --git a/libs/ardour/ardour/movable.h b/libs/ardour/ardour/movable.h
index 2428e24465..64ad637f2d 100644
--- a/libs/ardour/ardour/movable.h
+++ b/libs/ardour/ardour/movable.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libardour_movable_h__
-#define __libardour_movable_h__
+#pragma once
 
 namespace ARDOUR {
 
@@ -30,4 +29,3 @@ class LIBARDOUR_API Movable {
 
 }
 
-#endif /* __libardour_movable_h__ */
diff --git a/libs/ardour/ardour/msvc_libardour.h b/libs/ardour/ardour/msvc_libardour.h
index 607087e45f..06bbddf833 100644
--- a/libs/ardour/ardour/msvc_libardour.h
+++ b/libs/ardour/ardour/msvc_libardour.h
@@ -15,8 +15,7 @@
  * with this program; if not, write to the Free Software Foundation, Inc.,
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
-#ifndef __msvc_libardour_h__
-#define __msvc_libardour_h__
+#pragma once
 
 #include <ardour/libardour_visibility.h>
 #include <limits.h>
@@ -69,4 +68,3 @@ LIBARDOUR_API int    LIBARDOUR_APICALLTYPE readlink(const char *__restrict short
 }  // namespace ARDOUR
 
 #endif // COMPILER_MSVC
-#endif // __mavc_libardour_h__
diff --git a/libs/ardour/ardour/mtdm.h b/libs/ardour/ardour/mtdm.h
index 7cde5d0253..fc5910aa74 100644
--- a/libs/ardour/ardour/mtdm.h
+++ b/libs/ardour/ardour/mtdm.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libardour_mtdm_h__
-#define __libardour_mtdm_h__
+#pragma once
 
 #include <stddef.h>
 
@@ -71,4 +70,3 @@ private:
 	float  _peak;
 };
 
-#endif /* __libardour_mtdm_h__ */
diff --git a/libs/ardour/ardour/mute_control.h b/libs/ardour/ardour/mute_control.h
index 35dee6d63f..a364f5e364 100644
--- a/libs/ardour/ardour/mute_control.h
+++ b/libs/ardour/ardour/mute_control.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_mute_control_h__
-#define __ardour_mute_control_h__
+#pragma once
 
 #include <memory>
 #include <string>
@@ -83,4 +82,3 @@ private:
 
 } /* namespace */
 
-#endif /* __libardour_mute_control_h__ */
diff --git a/libs/ardour/ardour/mute_master.h b/libs/ardour/ardour/mute_master.h
index d8d55851bf..049ff0951c 100644
--- a/libs/ardour/ardour/mute_master.h
+++ b/libs/ardour/ardour/mute_master.h
@@ -19,8 +19,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_mute_master_h__
-#define __ardour_mute_master_h__
+#pragma once
 
 #include <string>
 
@@ -93,4 +92,3 @@ private:
 
 } // namespace ARDOUR
 
-#endif /*__ardour_mute_master_h__ */
diff --git a/libs/ardour/ardour/muteable.h b/libs/ardour/ardour/muteable.h
index cb2290d268..d3831e0b4f 100644
--- a/libs/ardour/ardour/muteable.h
+++ b/libs/ardour/ardour/muteable.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_muteable_h__
-#define __ardour_muteable_h__
+#pragma once
 
 #include <memory>
 
@@ -49,4 +48,3 @@ protected:
 
 } /* namespace */
 
-#endif /* __ardour_muteable_h__ */
diff --git a/libs/ardour/ardour/onset_detector.h b/libs/ardour/ardour/onset_detector.h
index b5e64d16a5..1a83fb321a 100644
--- a/libs/ardour/ardour/onset_detector.h
+++ b/libs/ardour/ardour/onset_detector.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_onset_detector_h__
-#define __ardour_onset_detector_h__
+#pragma once
 
 #include "ardour/audioanalyser.h"
 
@@ -53,4 +52,3 @@ protected:
 
 } /* namespace */
 
-#endif /* __ardour_audioanalyser_h__ */
diff --git a/libs/ardour/ardour/pan_controllable.h b/libs/ardour/ardour/pan_controllable.h
index 63b0d38388..2735f2d9d0 100644
--- a/libs/ardour/ardour/pan_controllable.h
+++ b/libs/ardour/ardour/pan_controllable.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libardour_pan_controllable_h__
-#define __libardour_pan_controllable_h__
+#pragma once
 
 #include <memory>
 #include <string>
@@ -54,4 +53,3 @@ class LIBARDOUR_API PanControllable : public AutomationControl
 
 } // namespace
 
-#endif /* __libardour_pan_controllable_h__ */
diff --git a/libs/ardour/ardour/pannable.h b/libs/ardour/ardour/pannable.h
index 1c3253fbec..5b7f878313 100644
--- a/libs/ardour/ardour/pannable.h
+++ b/libs/ardour/ardour/pannable.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libardour_pannable_h__
-#define __libardour_pannable_h__
+#pragma once
 
 #include <memory>
 #include <string>
@@ -97,4 +96,3 @@ private:
 
 } // namespace
 
-#endif /* __libardour_pannable_h__ */
diff --git a/libs/ardour/ardour/panner.h b/libs/ardour/ardour/panner.h
index ec323e8a2d..18aa319a77 100644
--- a/libs/ardour/ardour/panner.h
+++ b/libs/ardour/ardour/panner.h
@@ -20,8 +20,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_panner_h__
-#define __ardour_panner_h__
+#pragma once
 
 #include <cmath>
 #include <cassert>
@@ -167,4 +166,3 @@ struct LIBARDOUR_API PanPluginDescriptor {
 };
 }
 
-#endif /* __ardour_panner_h__ */
diff --git a/libs/ardour/ardour/panner_manager.h b/libs/ardour/ardour/panner_manager.h
index ec843c400d..14d3528e70 100644
--- a/libs/ardour/ardour/panner_manager.h
+++ b/libs/ardour/ardour/panner_manager.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_panner_manager_h__
-#define __ardour_panner_manager_h__
+#pragma once
 
 #include <map>
 #include <string>
@@ -69,4 +68,3 @@ private:
 
 } // namespace
 
-#endif /* __ardour_panner_manager_h__ */
diff --git a/libs/ardour/ardour/panner_shell.h b/libs/ardour/ardour/panner_shell.h
index 971a74d683..2b239dd687 100644
--- a/libs/ardour/ardour/panner_shell.h
+++ b/libs/ardour/ardour/panner_shell.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_panner_shell_h__
-#define __ardour_panner_shell_h__
+#pragma once
 
 #include <cmath>
 #include <cassert>
@@ -107,4 +106,3 @@ public:
 
 } // namespace ARDOUR
 
-#endif /* __ardour_panner_shell_h__ */
diff --git a/libs/ardour/ardour/parameter_descriptor.h b/libs/ardour/ardour/parameter_descriptor.h
index 92389ca621..9cbe441304 100644
--- a/libs/ardour/ardour/parameter_descriptor.h
+++ b/libs/ardour/ardour/parameter_descriptor.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_parameter_descriptor_h__
-#define __ardour_parameter_descriptor_h__
+#pragma once
 
 #include "pbd/natsort.h"
 #include "ardour/types.h"
@@ -125,4 +124,3 @@ struct LIBARDOUR_API ParameterDescriptor : public Evoral::ParameterDescriptor
 
 } // namespace ARDOUR
 
-#endif // __ardour_parameter_descriptor_h__
diff --git a/libs/ardour/ardour/parameter_types.h b/libs/ardour/ardour/parameter_types.h
index 5893956818..23286556c7 100644
--- a/libs/ardour/ardour/parameter_types.h
+++ b/libs/ardour/ardour/parameter_types.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_parameter_types_h__
-#define __ardour_parameter_types_h__
+#pragma once
 
 #include <stdint.h>
 
@@ -92,5 +91,4 @@ parameter_is_midi(Evoral::ParameterType t)
 
 }  // namespace ARDOUR
 
-#endif /* __ardour_parameter_types_h__ */
 
diff --git a/libs/ardour/ardour/peak.h b/libs/ardour/ardour/peak.h
index cec625915b..47668177e2 100644
--- a/libs/ardour/ardour/peak.h
+++ b/libs/ardour/ardour/peak.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_peak_h__
-#define __ardour_peak_h__
+#pragma once
 
 #include <cmath>
 #include "ardour/libardour_visibility.h"
@@ -34,4 +33,3 @@ default_compute_peak (const ARDOUR::Sample * const buf, ARDOUR::pframes_t nsampl
 	return current;
 }
 
-#endif /* __ardour_peak_h__ */
diff --git a/libs/ardour/ardour/phase_control.h b/libs/ardour/ardour/phase_control.h
index 8ce4e181ab..5516530597 100644
--- a/libs/ardour/ardour/phase_control.h
+++ b/libs/ardour/ardour/phase_control.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_phase_control_h__
-#define __ardour_phase_control_h__
+#pragma once
 
 #include <memory>
 #include <string>
@@ -68,4 +67,3 @@ class LIBARDOUR_API PhaseControl : public AutomationControl
 
 } /* namespace */
 
-#endif /* __libardour_phase_control_h__ */
diff --git a/libs/ardour/ardour/pitch.h b/libs/ardour/ardour/pitch.h
index 21823c76f5..254ca90e9e 100644
--- a/libs/ardour/ardour/pitch.h
+++ b/libs/ardour/ardour/pitch.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_pitch_h__
-#define __ardour_pitch_h__
+#pragma once
 
 #ifdef WAF_BUILD
 #include "libardour-config.h"
@@ -64,4 +63,3 @@ class LIBARDOUR_API Pitch : public Filter {
 
 #endif
 
-#endif /* __ardour_pitch_h__ */
diff --git a/libs/ardour/ardour/playlist.h b/libs/ardour/ardour/playlist.h
index 882c886845..ce042b8e35 100644
--- a/libs/ardour/ardour/playlist.h
+++ b/libs/ardour/ardour/playlist.h
@@ -24,8 +24,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_playlist_h__
-#define __ardour_playlist_h__
+#pragma once
 
 #include <atomic>
 #include <list>
@@ -481,5 +480,4 @@ private:
 
 } /* namespace ARDOUR */
 
-#endif /* __ardour_playlist_h__ */
 
diff --git a/libs/ardour/ardour/playlist_factory.h b/libs/ardour/ardour/playlist_factory.h
index 7e641dd418..5344958236 100644
--- a/libs/ardour/ardour/playlist_factory.h
+++ b/libs/ardour/ardour/playlist_factory.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_playlist_factory_h__
-#define __ardour_playlist_factory_h__
+#pragma once
 
 #include "ardour/playlist.h"
 
@@ -42,4 +41,3 @@ class LIBARDOUR_API PlaylistFactory {
 
 }
 
-#endif /* __ardour_playlist_factory_h__  */
diff --git a/libs/ardour/ardour/playlist_source.h b/libs/ardour/ardour/playlist_source.h
index f426c84a0e..540b57b003 100644
--- a/libs/ardour/ardour/playlist_source.h
+++ b/libs/ardour/ardour/playlist_source.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_playlist_source_h__
-#define __ardour_playlist_source_h__
+#pragma once
 
 #include <memory>
 #include <string>
@@ -56,4 +55,3 @@ protected:
 
 } /* namespace */
 
-#endif /* __ardour_playlist_source_h__ */
diff --git a/libs/ardour/ardour/plugin.h b/libs/ardour/ardour/plugin.h
index 01ad34f8a7..2eef4ea352 100644
--- a/libs/ardour/ardour/plugin.h
+++ b/libs/ardour/ardour/plugin.h
@@ -20,8 +20,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_plugin_h__
-#define __ardour_plugin_h__
+#pragma once
 
 #include <atomic>
 #include <memory>
@@ -546,4 +545,3 @@ protected:
 
 } // namespace ARDOUR
 
-#endif /* __ardour_plugin_h__ */
diff --git a/libs/ardour/ardour/plugin_insert.h b/libs/ardour/ardour/plugin_insert.h
index 5ad4192080..42a17ff5b6 100644
--- a/libs/ardour/ardour/plugin_insert.h
+++ b/libs/ardour/ardour/plugin_insert.h
@@ -21,8 +21,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_plugin_insert_h__
-#define __ardour_plugin_insert_h__
+#pragma once
 
 #include <atomic>
 #include <memory>
@@ -395,4 +394,3 @@ private:
 
 } // namespace ARDOUR
 
-#endif /* __ardour_plugin_insert_h__ */
diff --git a/libs/ardour/ardour/plugin_manager.h b/libs/ardour/ardour/plugin_manager.h
index 8716024d6f..661f1bfaa1 100644
--- a/libs/ardour/ardour/plugin_manager.h
+++ b/libs/ardour/ardour/plugin_manager.h
@@ -21,8 +21,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_plugin_manager_h__
-#define __ardour_plugin_manager_h__
+#pragma once
 
 #ifdef WAF_BUILD
 #include "libardour-config.h"
@@ -372,5 +371,4 @@ private:
 
 } /* namespace ARDOUR */
 
-#endif /* __ardour_plugin_manager_h__ */
 
diff --git a/libs/ardour/ardour/plugin_types.h b/libs/ardour/ardour/plugin_types.h
index 9ae5b9e2f7..09c75c7264 100644
--- a/libs/ardour/ardour/plugin_types.h
+++ b/libs/ardour/ardour/plugin_types.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_plugin_types_h__
-#define __ardour_plugin_types_h__
+#pragma once
 
 namespace ARDOUR {
 
@@ -33,4 +32,4 @@ namespace ARDOUR {
 	};
 
 }
-#endif
+
diff --git a/libs/ardour/ardour/port.h b/libs/ardour/ardour/port.h
index 3037b8f9da..d920266cad 100644
--- a/libs/ardour/ardour/port.h
+++ b/libs/ardour/ardour/port.h
@@ -19,8 +19,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_port_h__
-#define __ardour_port_h__
+#pragma once
 
 #ifdef WAF_BUILD
 #include "libardour-config.h"
@@ -228,4 +227,3 @@ private:
 
 }
 
-#endif /* __ardour_port_h__ */
diff --git a/libs/ardour/ardour/port_engine.h b/libs/ardour/ardour/port_engine.h
index 859158d0ca..f560ebb44d 100644
--- a/libs/ardour/ardour/port_engine.h
+++ b/libs/ardour/ardour/port_engine.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libardour_port_engine_h__
-#define __libardour_port_engine_h__
+#pragma once
 
 #include <vector>
 #include <string>
@@ -508,4 +507,3 @@ protected:
 
 } // namespace
 
-#endif /* __libardour_port_engine_h__ */
diff --git a/libs/ardour/ardour/port_insert.h b/libs/ardour/ardour/port_insert.h
index f69cf33162..0af5517732 100644
--- a/libs/ardour/ardour/port_insert.h
+++ b/libs/ardour/ardour/port_insert.h
@@ -19,8 +19,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_port_insert_h__
-#define __ardour_port_insert_h__
+#pragma once
 
 #include <vector>
 #include <string>
@@ -146,4 +145,3 @@ private:
 
 } // namespace ARDOUR
 
-#endif /* __ardour_port_insert_h__ */
diff --git a/libs/ardour/ardour/port_manager.h b/libs/ardour/ardour/port_manager.h
index 5009e7492c..a738d3f6b4 100644
--- a/libs/ardour/ardour/port_manager.h
+++ b/libs/ardour/ardour/port_manager.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libardour_port_manager_h__
-#define __libardour_port_manager_h__
+#pragma once
 
 #include <atomic>
 #include <cstdint>
@@ -393,4 +392,3 @@ private:
 
 } // namespace ARDOUR
 
-#endif /* __libardour_port_manager_h__ */
diff --git a/libs/ardour/ardour/port_set.h b/libs/ardour/ardour/port_set.h
index 98df046b0f..42557ac79c 100644
--- a/libs/ardour/ardour/port_set.h
+++ b/libs/ardour/ardour/port_set.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_port_set_h__
-#define __ardour_port_set_h__
+#pragma once
 
 #include <vector>
 #include "ardour/chan_count.h"
@@ -154,4 +153,3 @@ private:
 
 } // namespace ARDOUR
 
-#endif // __ardour_port_set_h__
diff --git a/libs/ardour/ardour/presentation_info.h b/libs/ardour/ardour/presentation_info.h
index c3736f8242..7e4f1d99d2 100644
--- a/libs/ardour/ardour/presentation_info.h
+++ b/libs/ardour/ardour/presentation_info.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libardour_presentation_info_h__
-#define __libardour_presentation_info_h__
+#pragma once
 
 #include <iostream>
 #include <string>
@@ -305,4 +304,3 @@ namespace std {
 std::ostream& operator<<(std::ostream& o, ARDOUR::PresentationInfo const& rid);
 }
 
-#endif /* __libardour_presentation_info_h__ */
diff --git a/libs/ardour/ardour/processor.h b/libs/ardour/ardour/processor.h
index 2b5402df24..cc8838ed77 100644
--- a/libs/ardour/ardour/processor.h
+++ b/libs/ardour/ardour/processor.h
@@ -19,8 +19,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_processor_h__
-#define __ardour_processor_h__
+#pragma once
 
 #include <vector>
 #include <string>
@@ -199,4 +198,3 @@ protected:
 
 } // namespace ARDOUR
 
-#endif /* __ardour_processor_h__ */
diff --git a/libs/ardour/ardour/profile.h b/libs/ardour/ardour/profile.h
index 33f6c05180..856d64d957 100644
--- a/libs/ardour/ardour/profile.h
+++ b/libs/ardour/ardour/profile.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_profile_h__
-#define __ardour_profile_h__
+#pragma once
 
 #include <boost/dynamic_bitset.hpp>
 #include <stdint.h>
@@ -60,4 +59,3 @@ LIBARDOUR_API extern RuntimeProfile* Profile;
 
 }; // namespace ARDOUR
 
-#endif /* __ardour_profile_h__ */
diff --git a/libs/ardour/ardour/proxy_controllable.h b/libs/ardour/ardour/proxy_controllable.h
index 6ed7ab91c7..93aa927307 100644
--- a/libs/ardour/ardour/proxy_controllable.h
+++ b/libs/ardour/ardour/proxy_controllable.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libardour_proxy_controllable_h__
-#define __libardour_proxy_controllable_h__
+#pragma once
 
 #include <boost/function.hpp>
 
@@ -55,4 +54,3 @@ class LIBARDOUR_API ProxyControllable : public PBD::Controllable {
 
 } // namespace
 
-#endif /* __libardour_proxy_controllable_h__ */
diff --git a/libs/ardour/ardour/quantize.h b/libs/ardour/ardour/quantize.h
index a2376abe69..8f5e972882 100644
--- a/libs/ardour/ardour/quantize.h
+++ b/libs/ardour/ardour/quantize.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_quantize_h__
-#define __ardour_quantize_h__
+#pragma once
 
 #include "ardour/libardour_visibility.h"
 #include "ardour/types.h"
@@ -56,4 +55,3 @@ private:
 
 } /* namespace */
 
-#endif /* __ardour_quantize_h__ */
diff --git a/libs/ardour/ardour/rb_effect.h b/libs/ardour/ardour/rb_effect.h
index 0232996828..5980d3828d 100644
--- a/libs/ardour/ardour/rb_effect.h
+++ b/libs/ardour/ardour/rb_effect.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_rbeffect_h__
-#define __ardour_rbeffect_h__
+#pragma once
 
 #include "ardour/filter.h"
 #include "ardour/timefx_request.h"
@@ -40,4 +39,3 @@ class LIBARDOUR_API RBEffect : public Filter {
 
 } /* namespace */
 
-#endif /* __ardour_rbeffect_h__ */
diff --git a/libs/ardour/ardour/rc_configuration.h b/libs/ardour/ardour/rc_configuration.h
index 688905fbf0..d8c660f2f6 100644
--- a/libs/ardour/ardour/rc_configuration.h
+++ b/libs/ardour/ardour/rc_configuration.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_rc_configuration_h__
-#define __ardour_rc_configuration_h__
+#pragma once
 
 #include <map>
 #include <string>
@@ -100,4 +99,3 @@ LIBARDOUR_API extern gain_t speed_quietning; /* see comment in configuration.cc
 
 } // namespace ARDOUR
 
-#endif /* __ardour_configuration_h__ */
diff --git a/libs/ardour/ardour/readable.h b/libs/ardour/ardour/readable.h
index 931488dcc4..8d220b5f95 100644
--- a/libs/ardour/ardour/readable.h
+++ b/libs/ardour/ardour/readable.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_readable_h__
-#define __ardour_readable_h__
+#pragma once
 
 #include "ardour/libardour_visibility.h"
 #include "ardour/types.h"
@@ -41,4 +40,3 @@ public:
 
 }
 
-#endif /* __ardour_readable_h__ */
diff --git a/libs/ardour/ardour/readonly_control.h b/libs/ardour/ardour/readonly_control.h
index 3a0dd6ebf1..ee92dbb629 100644
--- a/libs/ardour/ardour/readonly_control.h
+++ b/libs/ardour/ardour/readonly_control.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_readonly_control_h__
-#define __ardour_readonly_control_h__
+#pragma once
 
 #include <memory>
 
@@ -47,4 +46,3 @@ protected:
 
 } // namespace ARDOUR
 
-#endif /* __ardour_readonly_control_h__ */
diff --git a/libs/ardour/ardour/recent_sessions.h b/libs/ardour/ardour/recent_sessions.h
index 25738dece8..930b6c1f82 100644
--- a/libs/ardour/ardour/recent_sessions.h
+++ b/libs/ardour/ardour/recent_sessions.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_recent_sessions_h__
-#define __ardour_recent_sessions_h__
+#pragma once
 
 #include <deque>
 #include <utility>
@@ -37,4 +36,3 @@ namespace ARDOUR {
 	LIBARDOUR_API int remove_recent_sessions (const std::string& path);
 }; // namespace ARDOUR
 
-#endif // __ardour_recent_sessions_h__
diff --git a/libs/ardour/ardour/record_enable_control.h b/libs/ardour/ardour/record_enable_control.h
index 3e64cdbc4e..1f0095810c 100644
--- a/libs/ardour/ardour/record_enable_control.h
+++ b/libs/ardour/ardour/record_enable_control.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_record_enable_control_h__
-#define __ardour_record_enable_control_h__
+#pragma once
 
 #include <memory>
 #include <string>
@@ -56,4 +55,3 @@ class LIBARDOUR_API RecordEnableControl : public SlavableAutomationControl
 
 } /* namespace */
 
-#endif /* __libardour_record_enable_control_h__ */
diff --git a/libs/ardour/ardour/record_safe_control.h b/libs/ardour/ardour/record_safe_control.h
index 5ff9c4e531..cf161bccdf 100644
--- a/libs/ardour/ardour/record_safe_control.h
+++ b/libs/ardour/ardour/record_safe_control.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_record_safe_control_h__
-#define __ardour_record_safe_control_h__
+#pragma once
 
 #include <memory>
 #include <string>
@@ -46,4 +45,3 @@ class LIBARDOUR_API RecordSafeControl : public SlavableAutomationControl
 
 } /* namespace */
 
-#endif /* __libardour_record_enable_control_h__ */
diff --git a/libs/ardour/ardour/recordable.h b/libs/ardour/ardour/recordable.h
index 9c0de7c7f0..48c8b1092d 100644
--- a/libs/ardour/ardour/recordable.h
+++ b/libs/ardour/ardour/recordable.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_recordable_h__
-#define __ardour_recordable_h__
+#pragma once
 
 namespace ARDOUR {
 
@@ -32,4 +31,3 @@ class Recordable {
 
 } /* namespace */
 
-#endif /* __ardour_recordable_h__ */
diff --git a/libs/ardour/ardour/region.h b/libs/ardour/ardour/region.h
index 9313d84a2d..1d5d646449 100644
--- a/libs/ardour/ardour/region.h
+++ b/libs/ardour/ardour/region.h
@@ -21,8 +21,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_region_h__
-#define __ardour_region_h__
+#pragma once
 
 #include <memory>
 #include <vector>
@@ -679,4 +678,3 @@ private:
 
 } /* namespace ARDOUR */
 
-#endif /* __ardour_region_h__ */
diff --git a/libs/ardour/ardour/region_factory.h b/libs/ardour/ardour/region_factory.h
index 16bc56b7cd..79703dbff6 100644
--- a/libs/ardour/ardour/region_factory.h
+++ b/libs/ardour/ardour/region_factory.h
@@ -21,8 +21,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_region_factory_h__
-#define __ardour_region_factory_h__
+#pragma once
 
 #include <glibmm/threads.h>
 #include <map>
@@ -172,4 +171,3 @@ private:
 
 } // namespace ARDOUR
 
-#endif /* __ardour_region_factory_h__  */
diff --git a/libs/ardour/ardour/region_fx_plugin.h b/libs/ardour/ardour/region_fx_plugin.h
index 74e8c0fd50..babe655c61 100644
--- a/libs/ardour/ardour/region_fx_plugin.h
+++ b/libs/ardour/ardour/region_fx_plugin.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_region_fx_plugin_h__
-#define __ardour_region_fx_plugin_h__
+#pragma once
 
 #include <atomic>
 
@@ -207,4 +206,3 @@ private:
 
 } // namespace ARDOUR
 
-#endif
diff --git a/libs/ardour/ardour/region_sorters.h b/libs/ardour/ardour/region_sorters.h
index fc777997ad..59df02f931 100644
--- a/libs/ardour/ardour/region_sorters.h
+++ b/libs/ardour/ardour/region_sorters.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libardour_region_sorters_h__
-#define __libardour_region_sorters_h__
+#pragma once
 
 #include "ardour/region.h"
 
@@ -51,4 +50,3 @@ struct LIBARDOUR_API RegionSortByLayerAndPosition {
 
 } // namespace
 
-#endif /* __libardour_region_sorters_h__ */
diff --git a/libs/ardour/ardour/resampled_source.h b/libs/ardour/ardour/resampled_source.h
index 110069d50e..d23e3f5be5 100644
--- a/libs/ardour/ardour/resampled_source.h
+++ b/libs/ardour/ardour/resampled_source.h
@@ -19,8 +19,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_resampled_source_h__
-#define __ardour_resampled_source_h__
+#pragma once
 
 #include <samplerate.h>
 
@@ -63,4 +62,3 @@ class LIBARDOUR_API ResampledImportableSource : public ImportableSource
 
 }
 
-#endif /* __ardour_resampled_source_h__ */
diff --git a/libs/ardour/ardour/return.h b/libs/ardour/ardour/return.h
index fdb8fcff24..e56ddfb8d6 100644
--- a/libs/ardour/ardour/return.h
+++ b/libs/ardour/ardour/return.h
@@ -19,8 +19,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_return_h__
-#define __ardour_return_h__
+#pragma once
 
 #include <string>
 
@@ -77,5 +76,4 @@ private:
 
 } // namespace ARDOUR
 
-#endif /* __ardour_return_h__ */
 
diff --git a/libs/ardour/ardour/reverse.h b/libs/ardour/ardour/reverse.h
index 62faa6aeaa..d557ec1b56 100644
--- a/libs/ardour/ardour/reverse.h
+++ b/libs/ardour/ardour/reverse.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_reverse_h__
-#define __ardour_reverse_h__
+#pragma once
 
 #include "ardour/filter.h"
 
@@ -34,4 +33,3 @@ class LIBARDOUR_API Reverse : public Filter {
 
 } /* namespace */
 
-#endif /* __ardour_reverse_h__ */
diff --git a/libs/ardour/ardour/revision.h b/libs/ardour/ardour/revision.h
index 8e29a2d141..5a3f776844 100644
--- a/libs/ardour/ardour/revision.h
+++ b/libs/ardour/ardour/revision.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_revision_h__
-#define __ardour_revision_h__
+#pragma once
 
 #include "ardour/libardour_visibility.h"
 
@@ -30,4 +29,3 @@ namespace ARDOUR {
 	}
 }
 
-#endif
diff --git a/libs/ardour/ardour/route.h b/libs/ardour/ardour/route.h
index 2f270eb7d9..2e1be45087 100644
--- a/libs/ardour/ardour/route.h
+++ b/libs/ardour/ardour/route.h
@@ -21,8 +21,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_route_h__
-#define __ardour_route_h__
+#pragma once
 
 #include <atomic>
 #include <cmath>
@@ -811,4 +810,3 @@ private:
 
 } // namespace ARDOUR
 
-#endif /* __ardour_route_h__ */
diff --git a/libs/ardour/ardour/route_group.h b/libs/ardour/ardour/route_group.h
index 5aace6dac0..877d248c4e 100644
--- a/libs/ardour/ardour/route_group.h
+++ b/libs/ardour/ardour/route_group.h
@@ -21,8 +21,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_route_group_h__
-#define __ardour_route_group_h__
+#pragma once
 
 #include <list>
 #include <set>
@@ -209,4 +208,3 @@ private:
 
 } /* namespace */
 
-#endif /* __ardour_route_group_h__ */
diff --git a/libs/ardour/ardour/route_group_member.h b/libs/ardour/ardour/route_group_member.h
index 73f303b30a..bd6085d3ce 100644
--- a/libs/ardour/ardour/route_group_member.h
+++ b/libs/ardour/ardour/route_group_member.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libardour_route_group_member_h__
-#define __libardour_route_group_member_h__
+#pragma once
 
 #include "ardour/libardour_visibility.h"
 #include "pbd/controllable.h"
@@ -51,4 +50,3 @@ class LIBARDOUR_API RouteGroupMember
 
 }
 
-#endif /* __libardour_route_group_member_h__ */
diff --git a/libs/ardour/ardour/route_group_specialized.h b/libs/ardour/ardour/route_group_specialized.h
index ad21a6c3f3..9ec2eadfa3 100644
--- a/libs/ardour/ardour/route_group_specialized.h
+++ b/libs/ardour/ardour/route_group_specialized.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_route_group_specialized_h__
-#define __ardour_route_group_specialized_h__
+#pragma once
 
 #include "ardour/route_group.h"
 #include "ardour/track.h"
@@ -40,5 +39,4 @@ RouteGroup::apply (void (Track::*func)(T, PBD::Controllable::GroupControlDisposi
 
 } /* namespace ARDOUR */
 
-#endif /* __ardour_route_group_specialized_h__ */
 
diff --git a/libs/ardour/ardour/rt_midibuffer.h b/libs/ardour/ardour/rt_midibuffer.h
index 8efe49d898..a0411b08c9 100644
--- a/libs/ardour/ardour/rt_midibuffer.h
+++ b/libs/ardour/ardour/rt_midibuffer.h
@@ -20,8 +20,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_rt_midi_buffer_h__
-#define __ardour_rt_midi_buffer_h__
+#pragma once
 
 #include <map>
 
@@ -147,4 +146,3 @@ typedef RTMidiBufferBase<samplepos_t,samplecnt_t> RTMidiBuffer;
 
 } // namespace ARDOUR
 
-#endif // __ardour_rt_midi_buffer_h__
diff --git a/libs/ardour/ardour/runtime_functions.h b/libs/ardour/ardour/runtime_functions.h
index 7da8394616..b87e387cef 100644
--- a/libs/ardour/ardour/runtime_functions.h
+++ b/libs/ardour/ardour/runtime_functions.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_runtime_functions_h__
-#define __ardour_runtime_functions_h__
+#pragma once
 
 #include "ardour/libardour_visibility.h"
 #include "ardour/types.h"
@@ -40,4 +39,3 @@ namespace ARDOUR {
 	LIBARDOUR_API extern copy_vector_t           copy_vector;
 }
 
-#endif /* __ardour_runtime_functions_h__ */
diff --git a/libs/ardour/ardour/scene_change.h b/libs/ardour/ardour/scene_change.h
index 0cd57c5341..1e5a8ee3b0 100644
--- a/libs/ardour/ardour/scene_change.h
+++ b/libs/ardour/ardour/scene_change.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libardour_scene_change_h__
-#define __libardour_scene_change_h__
+#pragma once
 
 #include "pbd/stateful.h"
 
@@ -55,4 +54,3 @@ class SceneChange : public PBD::Stateful
 } /* namespace */
 
 
-#endif /* __libardour_scene_change_h__ */
diff --git a/libs/ardour/ardour/scene_changer.h b/libs/ardour/ardour/scene_changer.h
index d354d18d9b..7faeff7708 100644
--- a/libs/ardour/ardour/scene_changer.h
+++ b/libs/ardour/ardour/scene_changer.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libardour_scene_changer_h__
-#define __libardour_scene_changer_h__
+#pragma once
 
 #include <map>
 
@@ -52,4 +51,3 @@ class SceneChanger : public SessionHandleRef
 } /* namespace */
 
 
-#endif /* __libardour_scene_change_h__ */
diff --git a/libs/ardour/ardour/search_paths.h b/libs/ardour/ardour/search_paths.h
index cfcd14d522..fec185043f 100644
--- a/libs/ardour/ardour/search_paths.h
+++ b/libs/ardour/ardour/search_paths.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libardour_search_paths_h__
-#define __libardour_search_paths_h__
+#pragma once
 
 #include "ardour/libardour_visibility.h"
 
@@ -138,4 +137,3 @@ namespace ARDOUR {
 
 } // namespace ARDOUR
 
-#endif /* __libardour_search_paths_h__ */
diff --git a/libs/ardour/ardour/segment_descriptor.h b/libs/ardour/ardour/segment_descriptor.h
index 355f6c2b5f..a671480f33 100644
--- a/libs/ardour/ardour/segment_descriptor.h
+++ b/libs/ardour/ardour/segment_descriptor.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libardour_segment_descriptor_h__
-#define __libardour_segment_descriptor_h__
+#pragma once
 
 #include "temporal/timeline.h"
 #include "temporal/tempo.h"
@@ -84,4 +83,3 @@ private:
 
 }
 
-#endif /* __libardour_segment_descriptor_h__ */
diff --git a/libs/ardour/ardour/selection.h b/libs/ardour/ardour/selection.h
index 932f3b9855..33def1df82 100644
--- a/libs/ardour/ardour/selection.h
+++ b/libs/ardour/ardour/selection.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_selection_h__
-#define __ardour_selection_h__
+#pragma once
 
 #include <memory>
 #include <set>
@@ -131,4 +130,3 @@ class LIBARDOUR_API CoreSelection : public PBD::Stateful {
 
 } // namespace ARDOUR
 
-#endif /* __ardour_selection_h__ */
diff --git a/libs/ardour/ardour/send.h b/libs/ardour/ardour/send.h
index 0af592f94c..6b823200bd 100644
--- a/libs/ardour/ardour/send.h
+++ b/libs/ardour/ardour/send.h
@@ -20,8 +20,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_send_h__
-#define __ardour_send_h__
+#pragma once
 
 #include <string>
 
@@ -133,4 +132,3 @@ private:
 
 } // namespace ARDOUR
 
-#endif /* __ardour_send_h__ */
diff --git a/libs/ardour/ardour/session.h b/libs/ardour/ardour/session.h
index e9c6f192ae..a5d013c339 100644
--- a/libs/ardour/ardour/session.h
+++ b/libs/ardour/ardour/session.h
@@ -29,8 +29,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_session_h__
-#define __ardour_session_h__
+#pragma once
 
 #ifdef WAF_BUILD
 #include "libardour-config.h"
@@ -2360,4 +2359,3 @@ private:
 
 } // namespace ARDOUR
 
-#endif /* __ardour_session_h__ */
diff --git a/libs/ardour/ardour/session_configuration.h b/libs/ardour/ardour/session_configuration.h
index f100ca4667..5e2800cf47 100644
--- a/libs/ardour/ardour/session_configuration.h
+++ b/libs/ardour/ardour/session_configuration.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_session_configuration_h__
-#define __ardour_session_configuration_h__
+#pragma once
 
 #include <map>
 #include <string>
@@ -80,4 +79,3 @@ public:
 
 }
 
-#endif
diff --git a/libs/ardour/ardour/session_directory.h b/libs/ardour/ardour/session_directory.h
index dad96c40e5..48d1b9e471 100644
--- a/libs/ardour/ardour/session_directory.h
+++ b/libs/ardour/ardour/session_directory.h
@@ -20,8 +20,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_session_directory_h__
-#define __ardour_session_directory_h__
+#pragma once
 
 #include <string>
 #include <vector>
@@ -161,4 +160,3 @@ private:
 
 } // namespace ARDOUR
 
-#endif
diff --git a/libs/ardour/ardour/session_event.h b/libs/ardour/ardour/session_event.h
index 421990c82d..f7d34fbe2e 100644
--- a/libs/ardour/ardour/session_event.h
+++ b/libs/ardour/ardour/session_event.h
@@ -19,8 +19,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_session_event_h__
-#define __ardour_session_event_h__
+#pragma once
 
 #include <list>
 #include <memory>
@@ -202,4 +201,3 @@ protected:
 
 LIBARDOUR_API std::ostream& operator<<(std::ostream&, const ARDOUR::SessionEvent&);
 
-#endif /* __ardour_session_event_h__ */
diff --git a/libs/ardour/ardour/session_handle.h b/libs/ardour/ardour/session_handle.h
index 4dddb914d4..cf2e04dda5 100644
--- a/libs/ardour/ardour/session_handle.h
+++ b/libs/ardour/ardour/session_handle.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libardour_session_handle_h__
-#define __libardour_session_handle_h__
+#pragma once
 
 #include "pbd/signals.h"
 
@@ -57,4 +56,3 @@ class LIBARDOUR_API SessionHandlePtr
 
 } /* namespace */
 
-#endif /* __libardour_session_handle_h__ */
diff --git a/libs/ardour/ardour/session_metadata.h b/libs/ardour/ardour/session_metadata.h
index edc999a893..a38e15f92a 100644
--- a/libs/ardour/ardour/session_metadata.h
+++ b/libs/ardour/ardour/session_metadata.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_session_metadata_h__
-#define __ardour_session_metadata_h__
+#pragma once
 
 #include <string>
 
@@ -162,4 +161,3 @@ class LIBARDOUR_API SessionMetadata : public PBD::StatefulDestructible
 
 } // namespace ARDOUR
 
-#endif // __ardour_session_metadata_h__
diff --git a/libs/ardour/ardour/session_object.h b/libs/ardour/ardour/session_object.h
index 3897115598..fee9e66581 100644
--- a/libs/ardour/ardour/session_object.h
+++ b/libs/ardour/ardour/session_object.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_session_object_h__
-#define __ardour_session_object_h__
+#pragma once
 
 #include <string>
 #include "pbd/statefuldestructible.h"
@@ -72,4 +71,3 @@ class LIBARDOUR_API SessionObject : public SessionHandleRef, public PBD::Statefu
 
 } // namespace ARDOUR
 
-#endif /*__ardour_io_h__ */
diff --git a/libs/ardour/ardour/session_playlist.h b/libs/ardour/ardour/session_playlist.h
index 869cf0650e..1f76ab51a4 100644
--- a/libs/ardour/ardour/session_playlist.h
+++ b/libs/ardour/ardour/session_playlist.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_session_playlist_h__
-#define __ardour_session_playlist_h__
+#pragma once
 
 #include "ardour/session.h"
 #include "ardour/playlist.h"
@@ -45,4 +44,3 @@ SessionPlaylists::foreach (T *obj, void (T::*func)(std::shared_ptr<Playlist>))
 
 } /* namespace */
 
-#endif /* __ardour_session_playlist_h__ */
diff --git a/libs/ardour/ardour/session_playlists.h b/libs/ardour/ardour/session_playlists.h
index b68435436a..605e9a1753 100644
--- a/libs/ardour/ardour/session_playlists.h
+++ b/libs/ardour/ardour/session_playlists.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_session_playlists_h__
-#define __ardour_session_playlists_h__
+#pragma once
 
 #include <memory>
 #include <set>
@@ -100,4 +99,3 @@ private:
 
 }
 
-#endif
diff --git a/libs/ardour/ardour/session_route.h b/libs/ardour/ardour/session_route.h
index d63b50ac07..392b5ffd4d 100644
--- a/libs/ardour/ardour/session_route.h
+++ b/libs/ardour/ardour/session_route.h
@@ -19,8 +19,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_session_route_h__
-#define __ardour_session_route_h__
+#pragma once
 
 #include <iostream>
 
@@ -124,4 +123,3 @@ Session::foreach_route (void (Route::*method)(A1, A2), A1 arg1, A2 arg2)
 
 } /* namespace */
 
-#endif /* __ardour_session_route_h__ */
diff --git a/libs/ardour/ardour/session_utils.h b/libs/ardour/ardour/session_utils.h
index 2fe7f0480f..e24aa9376f 100644
--- a/libs/ardour/ardour/session_utils.h
+++ b/libs/ardour/ardour/session_utils.h
@@ -18,8 +18,7 @@
  */
 
 
-#ifndef __ardour_session_utils_h__
-#define __ardour_session_utils_h__
+#pragma once
 
 #include <string>
 
@@ -33,4 +32,3 @@ namespace ARDOUR {
 
 };
 
-#endif
diff --git a/libs/ardour/ardour/sidechain.h b/libs/ardour/ardour/sidechain.h
index 2ae315160b..f987c73dc6 100644
--- a/libs/ardour/ardour/sidechain.h
+++ b/libs/ardour/ardour/sidechain.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_sidechain_h__
-#define __ardour_sidechain_h__
+#pragma once
 
 #include <string>
 
@@ -50,4 +49,3 @@ private:
 
 } // namespace ARDOUR
 
-#endif // __ardour_sidechain_h__
diff --git a/libs/ardour/ardour/silentfilesource.h b/libs/ardour/ardour/silentfilesource.h
index 4895d8f13e..369fec496f 100644
--- a/libs/ardour/ardour/silentfilesource.h
+++ b/libs/ardour/ardour/silentfilesource.h
@@ -20,8 +20,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_silentfilesource_h__
-#define __ardour_silentfilesource_h__
+#pragma once
 
 #include <cstring>
 #include "ardour/audiofilesource.h"
@@ -74,5 +73,4 @@ protected:
 
 } // namespace ARDOUR
 
-#endif /* __ardour_audiofilesource_h__ */
 
diff --git a/libs/ardour/ardour/slavable.h b/libs/ardour/ardour/slavable.h
index df21ca1743..7d3b5594aa 100644
--- a/libs/ardour/ardour/slavable.h
+++ b/libs/ardour/ardour/slavable.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_slavable_h__
-#define __ardour_slavable_h__
+#pragma once
 
 #include <memory>
 #include <set>
@@ -89,4 +88,3 @@ private:
 
 } // namespace ARDOUR
 
-#endif /* __ardour_slavable_h__ */
diff --git a/libs/ardour/ardour/slavable_automation_control.h b/libs/ardour/ardour/slavable_automation_control.h
index db5b65855c..4b4b8d0c9f 100644
--- a/libs/ardour/ardour/slavable_automation_control.h
+++ b/libs/ardour/ardour/slavable_automation_control.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_slavable_automation_control_h__
-#define __ardour_slavable_automation_control_h__
+#pragma once
 
 #include "ardour/automation_control.h"
 #include "ardour/libardour_visibility.h"
@@ -157,4 +156,3 @@ protected:
 
 } // namespace ARDOUR
 
-#endif /* __ardour_slavable_automation_control_h__ */
diff --git a/libs/ardour/ardour/smf_source.h b/libs/ardour/ardour/smf_source.h
index 02994f55ea..07ecb2c53a 100644
--- a/libs/ardour/ardour/smf_source.h
+++ b/libs/ardour/ardour/smf_source.h
@@ -20,8 +20,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_smf_source_h__
-#define __ardour_smf_source_h__
+#pragma once
 
 #include <cstdio>
 #include <time.h>
@@ -118,4 +117,3 @@ public:
 
 }; /* namespace ARDOUR */
 
-#endif /* __ardour_smf_source_h__ */
diff --git a/libs/ardour/ardour/sndfile_helpers.h b/libs/ardour/ardour/sndfile_helpers.h
index d0454fbd29..e02caf505f 100644
--- a/libs/ardour/ardour/sndfile_helpers.h
+++ b/libs/ardour/ardour/sndfile_helpers.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __sndfile_helpers_h__
-#define __sndfile_helpers_h__
+#pragma once
 
 #include "ardour/types.h"
 
@@ -29,4 +28,3 @@ int sndfile_data_width (int format);
 std::string sndfile_major_format (int);
 std::string sndfile_minor_format (int);
 
-#endif /* __sndfile_helpers_h__ */
diff --git a/libs/ardour/ardour/sndfileimportable.h b/libs/ardour/ardour/sndfileimportable.h
index 62b7659977..b48da6ed80 100644
--- a/libs/ardour/ardour/sndfileimportable.h
+++ b/libs/ardour/ardour/sndfileimportable.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_sndfile_importable_source_h__
-#define __ardour_sndfile_importable_source_h__
+#pragma once
 
 #include <memory>
 
@@ -56,4 +55,3 @@ protected:
 
 }
 
-#endif /* __ardour_sndfile_importable_source_h__ */
diff --git a/libs/ardour/ardour/sndfilesource.h b/libs/ardour/ardour/sndfilesource.h
index f29de93872..33d372d4f9 100644
--- a/libs/ardour/ardour/sndfilesource.h
+++ b/libs/ardour/ardour/sndfilesource.h
@@ -22,8 +22,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __sndfile_source_h__
-#define __sndfile_source_h__
+#pragma once
 
 #include <sndfile.h>
 
@@ -104,5 +103,4 @@ class LIBARDOUR_API SndFileSource : public AudioFileSource {
 
 } // namespace ARDOUR
 
-#endif /* __sndfile_source_h__ */
 
diff --git a/libs/ardour/ardour/solo_control.h b/libs/ardour/ardour/solo_control.h
index 168e9a618c..927cc17e6f 100644
--- a/libs/ardour/ardour/solo_control.h
+++ b/libs/ardour/ardour/solo_control.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_solo_control_h__
-#define __ardour_solo_control_h__
+#pragma once
 
 #include <memory>
 #include <string>
@@ -115,4 +114,3 @@ class LIBARDOUR_API SoloControl : public SlavableAutomationControl
 
 } /* namespace */
 
-#endif /* __libardour_solo_control_h__ */
diff --git a/libs/ardour/ardour/solo_isolate_control.h b/libs/ardour/ardour/solo_isolate_control.h
index 7062d44d01..de499b9bc5 100644
--- a/libs/ardour/ardour/solo_isolate_control.h
+++ b/libs/ardour/ardour/solo_isolate_control.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_solo_isolate_control_h__
-#define __ardour_solo_isolate_control_h__
+#pragma once
 
 #include <memory>
 #include <string>
@@ -86,4 +85,3 @@ class LIBARDOUR_API SoloIsolateControl : public SlavableAutomationControl
 
 } /* namespace */
 
-#endif /* __libardour_solo_isolate_control_h__ */
diff --git a/libs/ardour/ardour/solo_safe_control.h b/libs/ardour/ardour/solo_safe_control.h
index 380f47f623..35c4617b9c 100644
--- a/libs/ardour/ardour/solo_safe_control.h
+++ b/libs/ardour/ardour/solo_safe_control.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_solo_safe_control_h__
-#define __ardour_solo_safe_control_h__
+#pragma once
 
 #include <string>
 
@@ -52,4 +51,3 @@ class LIBARDOUR_API SoloSafeControl : public SlavableAutomationControl
 
 } /* namespace */
 
-#endif /* __libardour_solo_safe_control_h__ */
diff --git a/libs/ardour/ardour/soloable.h b/libs/ardour/ardour/soloable.h
index 4b65aff244..c5038fe16b 100644
--- a/libs/ardour/ardour/soloable.h
+++ b/libs/ardour/ardour/soloable.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_soloable_h__
-#define __ardour_soloable_h__
+#pragma once
 
 #include <stdint.h>
 
@@ -36,4 +35,3 @@ class Soloable {
 
 } /* namespace */
 
-#endif /* __ardour_soloable_h__ */
diff --git a/libs/ardour/ardour/soundcloud_upload.h b/libs/ardour/ardour/soundcloud_upload.h
index bcf924738f..53a26f76d6 100644
--- a/libs/ardour/ardour/soundcloud_upload.h
+++ b/libs/ardour/ardour/soundcloud_upload.h
@@ -4,8 +4,7 @@
 
 *****************************************************************************/
 
-#ifndef __ardour_soundcloud_upload_h__
-#define __ardour_soundcloud_upload_h__
+#pragma once
 
 #include <string>
 #include <stdio.h>
@@ -50,4 +49,3 @@ private:
 
 };
 
-#endif /* __ardour_soundcloud_upload_h__ */
diff --git a/libs/ardour/ardour/soundseq.h b/libs/ardour/ardour/soundseq.h
index a261b78d08..2cf8bcc866 100644
--- a/libs/ardour/ardour/soundseq.h
+++ b/libs/ardour/ardour/soundseq.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __soundseq_h__
-#define __soundseq_h__
+#pragma once
 
 #include "edl.h"
 
@@ -46,7 +45,6 @@ class LIBARDOUR_API SoundPlaylist : public EDL::Playlist {
 
 } /* namespace ARDOUR */
 
-#endif /* __soundseq_h__ */
 
 
 
diff --git a/libs/ardour/ardour/source.h b/libs/ardour/ardour/source.h
index a74a90a4c2..cf64469895 100644
--- a/libs/ardour/ardour/source.h
+++ b/libs/ardour/ardour/source.h
@@ -20,8 +20,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_source_h__
-#define __ardour_source_h__
+#pragma once
 
 #include <atomic>
 #include <memory>
@@ -183,4 +182,3 @@ public:
 
 }
 
-#endif /* __ardour_source_h__ */
diff --git a/libs/ardour/ardour/source_factory.h b/libs/ardour/ardour/source_factory.h
index 0b9aee034a..1f488ad1f9 100644
--- a/libs/ardour/ardour/source_factory.h
+++ b/libs/ardour/ardour/source_factory.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_source_factory_h__
-#define __ardour_source_factory_h__
+#pragma once
 
 #include <memory>
 #include <stdint.h>
@@ -64,4 +63,3 @@ public:
 
 } // namespace ARDOUR
 
-#endif /* __ardour_source_factory_h__ */
diff --git a/libs/ardour/ardour/speaker.h b/libs/ardour/ardour/speaker.h
index f776026c3d..a7dd654f05 100644
--- a/libs/ardour/ardour/speaker.h
+++ b/libs/ardour/ardour/speaker.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libardour_speaker_h__
-#define __libardour_speaker_h__
+#pragma once
 
 #include "pbd/cartesian.h"
 #include "pbd/signals.h"
@@ -50,4 +49,3 @@ private:
 
 } /* namespace */
 
-#endif /* __libardour_speaker_h__ */
diff --git a/libs/ardour/ardour/speakers.h b/libs/ardour/ardour/speakers.h
index 3bcb117b62..f6f8beb506 100644
--- a/libs/ardour/ardour/speakers.h
+++ b/libs/ardour/ardour/speakers.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libardour_speakers_h__
-#define __libardour_speakers_h__
+#pragma once
 
 #include <vector>
 #include <iostream>
@@ -65,4 +64,3 @@ protected:
 
 } /* namespace */
 
-#endif /* __libardour_speakers_h__ */
diff --git a/libs/ardour/ardour/spline.h b/libs/ardour/ardour/spline.h
index d4dcf08d8a..c0f02180b7 100644
--- a/libs/ardour/ardour/spline.h
+++ b/libs/ardour/ardour/spline.h
@@ -17,8 +17,7 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
-#ifndef __ardour_spline_h__
-#define __ardour_spline_h__
+#pragma once
 
 #ifdef __cplusplus
 extern "C" {
@@ -86,4 +85,3 @@ struct LIBARDOUR_API _spline
 }
 #endif
 
-#endif /* __ardour_spline_h__ */
diff --git a/libs/ardour/ardour/srcfilesource.h b/libs/ardour/ardour/srcfilesource.h
index 5dd5e49b5a..f027f4b327 100644
--- a/libs/ardour/ardour/srcfilesource.h
+++ b/libs/ardour/ardour/srcfilesource.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_srcfilesource_h__
-#define __ardour_srcfilesource_h__
+#pragma once
 
 #include <cstring>
 #include <samplerate.h>
@@ -78,5 +77,4 @@ private:
 
 } // namespace ARDOUR
 
-#endif /* __ardour_audiofilesource_h__ */
 
diff --git a/libs/ardour/ardour/step_sequencer.h b/libs/ardour/ardour/step_sequencer.h
index 33d34885b3..6edfcdfd1e 100644
--- a/libs/ardour/ardour/step_sequencer.h
+++ b/libs/ardour/ardour/step_sequencer.h
@@ -16,8 +16,7 @@
  * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  */
 
-#ifndef __libardour_step_sequencer_h__
-#define __libardour_step_sequencer_h__
+#pragma once
 
 #include <vector>
 #include <unistd.h>
@@ -351,4 +350,3 @@ class StepSequencer : public PBD::Stateful
 
 } /* namespace */
 
-#endif /* __libardour_step_sequencer_h__ */
diff --git a/libs/ardour/ardour/stretch.h b/libs/ardour/ardour/stretch.h
index c045571125..01048d4f05 100644
--- a/libs/ardour/ardour/stretch.h
+++ b/libs/ardour/ardour/stretch.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_stretch_h__
-#define __ardour_stretch_h__
+#pragma once
 
 #ifdef WAF_BUILD
 #include "libardour-config.h"
@@ -60,4 +59,3 @@ class LIBARDOUR_API STStretch : public Filter {
 #endif
 
 
-#endif /* __ardour_stretch_h__ */
diff --git a/libs/ardour/ardour/stripable.h b/libs/ardour/ardour/stripable.h
index 0af0f48ef5..d4b4695c2d 100644
--- a/libs/ardour/ardour/stripable.h
+++ b/libs/ardour/ardour/stripable.h
@@ -19,8 +19,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libardour_stripable_h__
-#define __libardour_stripable_h__
+#pragma once
 
 #include <cstdint>
 #include <memory>
@@ -192,4 +191,3 @@ class LIBARDOUR_API Stripable : public SessionObject,
 
 }
 
-#endif /* __libardour_stripable_h__ */
diff --git a/libs/ardour/ardour/surround_return.h b/libs/ardour/ardour/surround_return.h
index d161a54907..ebe73f53a6 100644
--- a/libs/ardour/ardour/surround_return.h
+++ b/libs/ardour/ardour/surround_return.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_surround_return_h__
-#define __ardour_surround_return_h__
+#pragma once
 
 #ifdef HAVE_LV2_1_18_6
 #include <lv2/atom/atom.h>
@@ -203,4 +202,3 @@ private:
 
 } // namespace ARDOUR
 
-#endif /* __ardour_surround_return_h__ */
diff --git a/libs/ardour/ardour/surround_send.h b/libs/ardour/ardour/surround_send.h
index e7746fe35c..cbd01a44d8 100644
--- a/libs/ardour/ardour/surround_send.h
+++ b/libs/ardour/ardour/surround_send.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_surround_send_h__
-#define __ardour_surround_send_h__
+#pragma once
 
 #include "ardour/processor.h"
 #include "ardour/send.h"
@@ -104,4 +103,3 @@ private:
 
 } // namespace ARDOUR
 
-#endif /* __ardour_surround_send_h__ */
diff --git a/libs/ardour/ardour/tailtime.h b/libs/ardour/ardour/tailtime.h
index f0e6c038cf..6f0d81a69e 100644
--- a/libs/ardour/ardour/tailtime.h
+++ b/libs/ardour/ardour/tailtime.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_tailtime_h__
-#define __ardour_tailtime_h__
+#pragma once
 
 #include "pbd/signals.h"
 
@@ -65,5 +64,4 @@ private:
 } /* namespace */
 
 
-#endif /* __ardour_tailtime_h__*/
 
diff --git a/libs/ardour/ardour/tempo.h b/libs/ardour/ardour/tempo.h
index 297047c691..efbff19d8b 100644
--- a/libs/ardour/ardour/tempo.h
+++ b/libs/ardour/ardour/tempo.h
@@ -1,6 +1,4 @@
-#ifndef __ardour_tempo_h__
-#define __ardour_tempo_h__
+#pragma once
 
 #include "temporal/tempo.h"
 
-#endif /* __ardour_tempo_h__ */
diff --git a/libs/ardour/ardour/tempo_map_importer.h b/libs/ardour/ardour/tempo_map_importer.h
index eba6513b33..7ffacaf979 100644
--- a/libs/ardour/ardour/tempo_map_importer.h
+++ b/libs/ardour/ardour/tempo_map_importer.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_tempo_map_importer_h__
-#define __ardour_tempo_map_importer_h__
+#pragma once
 
 #include <memory>
 
@@ -58,4 +57,3 @@ class LIBARDOUR_API TempoMapImporter : public ElementImporter
 
 } // namespace ARDOUR
 
-#endif
diff --git a/libs/ardour/ardour/thawlist.h b/libs/ardour/ardour/thawlist.h
index 419dc77bee..8d8d76c515 100644
--- a/libs/ardour/ardour/thawlist.h
+++ b/libs/ardour/ardour/thawlist.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_thawlist_h__
-#define __ardour_thawlist_h__
+#pragma once
 
 #include "ardour/types.h"
 #include "ardour/libardour_visibility.h"
@@ -33,4 +32,4 @@ class LIBARDOUR_API ThawList : public RegionList
 };
 
 }
-#endif
+
diff --git a/libs/ardour/ardour/ticker.h b/libs/ardour/ardour/ticker.h
index f57ed65a91..cf343924dd 100644
--- a/libs/ardour/ardour/ticker.h
+++ b/libs/ardour/ardour/ticker.h
@@ -29,8 +29,7 @@
 #include "ardour/session_handle.h"
 #include "ardour/types.h"
 
-#ifndef __libardour_ticker_h__
-#define __libardour_ticker_h__
+#pragma once
 
 namespace ARDOUR
 {
@@ -69,4 +68,3 @@ private:
 
 } // namespace ARDOUR
 
-#endif /* __libardour_ticker_h__ */
diff --git a/libs/ardour/ardour/timecode.h b/libs/ardour/ardour/timecode.h
index 85dd3acf1a..a83810285e 100644
--- a/libs/ardour/ardour/timecode.h
+++ b/libs/ardour/ardour/timecode.h
@@ -17,9 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libardour_timecode_h__
-#define __libardour_timecode_h__
+#pragma once
 
 #include "temporal/time.h"
 
-#endif  // __libardour_timecode_h__
diff --git a/libs/ardour/ardour/timefx_request.h b/libs/ardour/ardour/timefx_request.h
index 033e32179c..3b53f575e8 100644
--- a/libs/ardour/ardour/timefx_request.h
+++ b/libs/ardour/ardour/timefx_request.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libardour_timefx_request_h__
-#define __libardour_timefx_request_h__
+#pragma once
 
 #include "temporal/types.h"
 #include "ardour/interthread_info.h"
@@ -44,4 +43,3 @@ namespace ARDOUR {
 	};
 }
 
-#endif /* __libardour_timefx_request_h__ */
diff --git a/libs/ardour/ardour/timestamps.h b/libs/ardour/ardour/timestamps.h
index 17d2f58f0a..ba617959db 100644
--- a/libs/ardour/ardour/timestamps.h
+++ b/libs/ardour/ardour/timestamps.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_timestamps_h__
-#define __ardour_timestamps_h__
+#pragma once
 
 #ifdef WITH_JACK_TIMESTAMPS
 #include <jack/timestamps.h>
@@ -28,4 +27,3 @@
 #define jack_reset_timestamps()
 #endif
 
-#endif /* __ardour_timestamps_h__ */
diff --git a/libs/ardour/ardour/track.h b/libs/ardour/ardour/track.h
index 8d84957d95..0866bab465 100644
--- a/libs/ardour/ardour/track.h
+++ b/libs/ardour/ardour/track.h
@@ -19,8 +19,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_track_h__
-#define __ardour_track_h__
+#pragma once
 
 #include <boost/optional.hpp>
 #include <memory>
@@ -258,4 +257,3 @@ namespace PBD {
 	DEFINE_ENUM_CONVERT(ARDOUR::Track::FreezeState);
 }
 
-#endif /* __ardour_track_h__ */
diff --git a/libs/ardour/ardour/transform.h b/libs/ardour/ardour/transform.h
index 95ba079529..57e8ea9400 100644
--- a/libs/ardour/ardour/transform.h
+++ b/libs/ardour/ardour/transform.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_transform_h__
-#define __ardour_transform_h__
+#pragma once
 
 #include <stack>
 #include <string>
@@ -143,4 +142,3 @@ private:
 
 } /* namespace */
 
-#endif /* __ardour_transform_h__ */
diff --git a/libs/ardour/ardour/transient_detector.h b/libs/ardour/ardour/transient_detector.h
index 129181dab5..55f692e150 100644
--- a/libs/ardour/ardour/transient_detector.h
+++ b/libs/ardour/ardour/transient_detector.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_transient_detector_h__
-#define __ardour_transient_detector_h__
+#pragma once
 
 #include "ardour/audioanalyser.h"
 
@@ -54,4 +53,3 @@ protected:
 
 } /* namespace */
 
-#endif /* __ardour_audioanalyser_h__ */
diff --git a/libs/ardour/ardour/transport_master.h b/libs/ardour/ardour/transport_master.h
index 9752636469..16f141d469 100644
--- a/libs/ardour/ardour/transport_master.h
+++ b/libs/ardour/ardour/transport_master.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_transport_master_h__
-#define __ardour_transport_master_h__
+#pragma once
 
 #include <vector>
 
@@ -779,4 +778,3 @@ private:
 
 }
 
-#endif /* __ardour_transport_master_h__ */
diff --git a/libs/ardour/ardour/transport_master_manager.h b/libs/ardour/ardour/transport_master_manager.h
index a67b7a122c..2a8f20c27c 100644
--- a/libs/ardour/ardour/transport_master_manager.h
+++ b/libs/ardour/ardour/transport_master_manager.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_transport_master_manager_h__
-#define __ardour_transport_master_manager_h__
+#pragma once
 
 #include <string>
 
@@ -132,4 +131,3 @@ class LIBARDOUR_API TransportMasterManager : public boost::noncopyable
 
 } // namespace ARDOUR
 
-#endif /* __ardour_transport_master_manager_h__ */
diff --git a/libs/ardour/ardour/transpose.h b/libs/ardour/ardour/transpose.h
index 416d9f7324..faf72a670d 100644
--- a/libs/ardour/ardour/transpose.h
+++ b/libs/ardour/ardour/transpose.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_transpose_h__
-#define __ardour_transpose_h__
+#pragma once
 
 #include "ardour/libardour_visibility.h"
 #include "ardour/midi_model.h"
@@ -44,4 +43,3 @@ private:
 
 } /* namespace */
 
-#endif /* __ardour_transpose_h__ */
diff --git a/libs/ardour/ardour/triggerbox.h b/libs/ardour/ardour/triggerbox.h
index 6a5b9d0933..372633d6c6 100644
--- a/libs/ardour/ardour/triggerbox.h
+++ b/libs/ardour/ardour/triggerbox.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_triggerbox_h__
-#define __ardour_triggerbox_h__
+#pragma once
 
 #include <pthread.h>
 
@@ -1031,4 +1030,3 @@ DEFINE_ENUM_CONVERT(ARDOUR::Trigger::StretchMode);
 } /* namespace PBD */
 
 
-#endif /* __ardour_triggerbox_h__ */
diff --git a/libs/ardour/ardour/trimmable.h b/libs/ardour/ardour/trimmable.h
index 0b92c66dab..357f812277 100644
--- a/libs/ardour/ardour/trimmable.h
+++ b/libs/ardour/ardour/trimmable.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libardour_trimmable_h__
-#define __libardour_trimmable_h__
+#pragma once
 
 namespace ARDOUR {
 
@@ -51,4 +50,3 @@ class LIBARDOUR_API Trimmable {
 
 }
 
-#endif /* __libardour_trimmable_h__ */
diff --git a/libs/ardour/ardour/types.h b/libs/ardour/ardour/types.h
index 5e20adc914..70626e5054 100644
--- a/libs/ardour/ardour/types.h
+++ b/libs/ardour/ardour/types.h
@@ -28,8 +28,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_types_h__
-#define __ardour_types_h__
+#pragma once
 
 #include <bitset>
 #include <cstdint>
@@ -991,4 +990,3 @@ enum SelectionOperation {
 
 using ARDOUR::samplepos_t;
 
-#endif /* __ardour_types_h__ */
diff --git a/libs/ardour/ardour/unknown_processor.h b/libs/ardour/ardour/unknown_processor.h
index 56dd4080ce..04e6dda3c3 100644
--- a/libs/ardour/ardour/unknown_processor.h
+++ b/libs/ardour/ardour/unknown_processor.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_unknown_processor_h__
-#define __ardour_unknown_processor_h__
+#pragma once
 
 #include "ardour/libardour_visibility.h"
 #include "ardour/processor.h"
@@ -67,4 +66,3 @@ private:
 
 }
 
-#endif
diff --git a/libs/ardour/ardour/uri_map.h b/libs/ardour/ardour/uri_map.h
index 8b80627daf..3e75fa34bd 100644
--- a/libs/ardour/ardour/uri_map.h
+++ b/libs/ardour/ardour/uri_map.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_uri_map_h__
-#define __ardour_uri_map_h__
+#pragma once
 
 #include <map>
 
@@ -149,4 +148,3 @@ private:
 
 } // namespace ARDOUR
 
-#endif // __ardour_uri_map_h__
diff --git a/libs/ardour/ardour/user_bundle.h b/libs/ardour/ardour/user_bundle.h
index 0161685706..941c1cf917 100644
--- a/libs/ardour/ardour/user_bundle.h
+++ b/libs/ardour/ardour/user_bundle.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_user_bundle_h__
-#define __ardour_user_bundle_h__
+#pragma once
 
 #include <vector>
 #include <glibmm/threads.h>
@@ -43,4 +42,3 @@ class LIBARDOUR_API UserBundle : public Bundle, public PBD::Stateful {
 
 }
 
-#endif
diff --git a/libs/ardour/ardour/utils.h b/libs/ardour/ardour/utils.h
index 337df374d2..73b3ccc0d6 100644
--- a/libs/ardour/ardour/utils.h
+++ b/libs/ardour/ardour/utils.h
@@ -21,8 +21,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_utils_h__
-#define __ardour_utils_h__
+#pragma once
 
 #ifdef WAF_BUILD
 #include "libardour-config.h"
@@ -153,4 +152,3 @@ LIBARDOUR_API std::string CFStringRefToStdString(CFStringRef stringRef);
 
 } //namespave
 
-#endif /* __ardour_utils_h__ */
diff --git a/libs/ardour/ardour/value_as_string.h b/libs/ardour/ardour/value_as_string.h
index daa430c4e6..5ff69a9422 100644
--- a/libs/ardour/ardour/value_as_string.h
+++ b/libs/ardour/ardour/value_as_string.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_value_as_string_h__
-#define __ardour_value_as_string_h__
+#pragma once
 
 #include <stddef.h>
 
@@ -93,4 +92,3 @@ value_as_string(const ARDOUR::ParameterDescriptor& desc,
 
 }  // namespace ARDOUR
 
-#endif /* __ardour_value_as_string_h__ */
diff --git a/libs/ardour/ardour/variant.h b/libs/ardour/ardour/variant.h
index 7e3f339471..a12544a961 100644
--- a/libs/ardour/ardour/variant.h
+++ b/libs/ardour/ardour/variant.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_variant_h__
-#define __ardour_variant_h__
+#pragma once
 
 #include <stdint.h>
 #include <limits.h>
@@ -217,4 +216,3 @@ private:
 
 } // namespace ARDOUR
 
-#endif // __ardour_variant_h__
diff --git a/libs/ardour/ardour/vca.h b/libs/ardour/ardour/vca.h
index b660e6ffb8..c3d8b5be8c 100644
--- a/libs/ardour/ardour/vca.h
+++ b/libs/ardour/ardour/vca.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_vca_h__
-#define __ardour_vca_h__
+#pragma once
 
 #include <memory>
 #include <string>
@@ -166,4 +165,3 @@ class LIBARDOUR_API VCA : public Stripable,
 
 } /* namespace */
 
-#endif /* __ardour_vca_h__ */
diff --git a/libs/ardour/ardour/vca_manager.h b/libs/ardour/ardour/vca_manager.h
index 58b68981b3..f51625d52c 100644
--- a/libs/ardour/ardour/vca_manager.h
+++ b/libs/ardour/ardour/vca_manager.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libardour_vca_manager_h__
-#define __libardour_vca_manager_h__
+#pragma once
 
 #include <string>
 #include <list>
@@ -74,4 +73,3 @@ private:
 
 } // namespace
 
-#endif /* __libardour_vca_manager_h__ */
diff --git a/libs/ardour/ardour/velocity_control.h b/libs/ardour/ardour/velocity_control.h
index 5c4c6b7fb8..3e4d461f57 100644
--- a/libs/ardour/ardour/velocity_control.h
+++ b/libs/ardour/ardour/velocity_control.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_velocity_control_h__
-#define __ardour_velocity_control_h__
+#pragma once
 
 #include <string>
 
@@ -39,4 +38,3 @@ class LIBARDOUR_API VelocityControl : public SlavableAutomationControl {
 
 } /* namespace */
 
-#endif /* __ardour_velocity_control_h__ */
diff --git a/libs/ardour/ardour/vst_plugin.h b/libs/ardour/ardour/vst_plugin.h
index 6b71d23131..e3398fec77 100644
--- a/libs/ardour/ardour/vst_plugin.h
+++ b/libs/ardour/ardour/vst_plugin.h
@@ -19,8 +19,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_vst_plugin_h__
-#define __ardour_vst_plugin_h__
+#pragma once
 
 #include <pbd/signals.h>
 #include "ardour/plugin.h"
@@ -143,4 +142,3 @@ protected:
 
 }
 
-#endif
diff --git a/libs/ardour/ardour/vst_types.h b/libs/ardour/ardour/vst_types.h
index 33687e6987..af7a2b34e9 100644
--- a/libs/ardour/ardour/vst_types.h
+++ b/libs/ardour/ardour/vst_types.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_vst_types_h__
-#define __ardour_vst_types_h__
+#pragma once
 
 #include <pthread.h>
 #include "ardour/libardour_visibility.h"
@@ -139,4 +138,3 @@ LIBARDOUR_API extern void vststate_maybe_set_program (VSTState* state);
 }
 #endif
 
-#endif
diff --git a/libs/ardour/ardour/windows_vst_plugin.h b/libs/ardour/ardour/windows_vst_plugin.h
index 0881eedf90..d79eafd8d7 100644
--- a/libs/ardour/ardour/windows_vst_plugin.h
+++ b/libs/ardour/ardour/windows_vst_plugin.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_windows_vst_plugin_h__
-#define __ardour_windows_vst_plugin_h__
+#pragma once
 
 #include "ardour/vst_plugin.h"
 
@@ -53,4 +52,3 @@ public:
 
 } // namespace ARDOUR
 
-#endif /* __ardour_vst_plugin_h__ */
diff --git a/libs/ardour/ardour/worker.h b/libs/ardour/ardour/worker.h
index 80cd1d374c..058c7a7e4b 100644
--- a/libs/ardour/ardour/worker.h
+++ b/libs/ardour/ardour/worker.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_worker_h__
-#define __ardour_worker_h__
+#pragma once
 
 #include <stdint.h>
 
@@ -116,4 +115,3 @@ private:
 
 } // namespace ARDOUR
 
-#endif  /* __ardour_worker_h__ */
diff --git a/libs/ardour/ardour/wrong_program.h b/libs/ardour/ardour/wrong_program.h
index 9e3bedce35..109992e3bd 100644
--- a/libs/ardour/ardour/wrong_program.h
+++ b/libs/ardour/ardour/wrong_program.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libardour_wrong_program_h__
-#define __libardour_wrong_program_h__
+#pragma once
 
 #include <exception>
 #include <string>
@@ -38,4 +37,3 @@ class LIBARDOUR_API WrongProgram : public std::exception {
 
 } /* namespace */
 
-#endif /* __libardour_wrong_program_h__ */
diff --git a/libs/ardouralsautil/ardouralsautil/deviceinfo.h b/libs/ardouralsautil/ardouralsautil/deviceinfo.h
index 3ccdb66e8e..619ee169a4 100644
--- a/libs/ardouralsautil/ardouralsautil/deviceinfo.h
+++ b/libs/ardouralsautil/ardouralsautil/deviceinfo.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libardouralsautil_deviceinfo_h__
-#define __libardouralsautil_deviceinfo_h__
+#pragma once
 
 namespace ARDOUR {
 
@@ -31,4 +30,3 @@ namespace ARDOUR {
 
 	int get_alsa_device_parameters (const char* device_name, const bool play, ALSADeviceInfo *nfo);
 }
-#endif
diff --git a/libs/ardouralsautil/ardouralsautil/devicelist.h b/libs/ardouralsautil/ardouralsautil/devicelist.h
index c29e3796eb..69182714fd 100644
--- a/libs/ardouralsautil/ardouralsautil/devicelist.h
+++ b/libs/ardouralsautil/ardouralsautil/devicelist.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libardouralsautil_devicelist_h__
-#define __libardouralsautil_devicelist_h__
+#pragma once
 
 #include <string>
 #include <map>
@@ -34,4 +33,3 @@ namespace ARDOUR {
 	int card_to_num(const char* device_name);
 
 }
-#endif
diff --git a/libs/audiographer/audiographer/visibility.h b/libs/audiographer/audiographer/visibility.h
index e475ad8c9e..b568d453d8 100644
--- a/libs/audiographer/audiographer/visibility.h
+++ b/libs/audiographer/audiographer/visibility.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libaudiographer_visibility_h__
-#define __libaudiographer_visibility_h__
+#pragma once
 
 #if defined(COMPILER_MSVC)
   #define LIBAUDIOGRAPHER_DLL_IMPORT __declspec(dllimport)
@@ -41,4 +40,3 @@
   #define LIBAUDIOGRAPHER_LOCAL LIBAUDIOGRAPHER_DLL_LOCAL
 #endif
 
-#endif /* __libaudiographer_visibility_h__ */
diff --git a/libs/evoral/evoral/visibility.h b/libs/evoral/evoral/visibility.h
index 40c503555c..26843021b4 100644
--- a/libs/evoral/evoral/visibility.h
+++ b/libs/evoral/evoral/visibility.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libevoral_visibility_h__
-#define __libevoral_visibility_h__
+#pragma once
 
 #if defined(COMPILER_MSVC)
   #define LIBEVORAL_DLL_IMPORT __declspec(dllimport)
@@ -47,4 +46,3 @@
   #define     LIBEVORAL_LOCAL LIBEVORAL_DLL_LOCAL
 #endif
 
-#endif /* __libevoral_visibility_h__ */
diff --git a/libs/gtkmm2ext/gtkmm2ext/doi.h b/libs/gtkmm2ext/gtkmm2ext/doi.h
index eda7406235..b8865737fd 100644
--- a/libs/gtkmm2ext/gtkmm2ext/doi.h
+++ b/libs/gtkmm2ext/gtkmm2ext/doi.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_gtk_doi_h__
-#define __ardour_gtk_doi_h__
+#pragma once
 
 #ifdef interface
 #undef interface
@@ -41,4 +40,3 @@ template<typename T> /*LIBGTKMM2EXT_API*/ gint delete_on_unmap (GdkEventAny *ign
 	return FALSE;
 }
 
-#endif /* __ardour_gtk_doi_h__ */
diff --git a/libs/gtkmm2ext/gtkmm2ext/gtk_ui.h b/libs/gtkmm2ext/gtkmm2ext/gtk_ui.h
index 718c8cec74..1d6b36088b 100644
--- a/libs/gtkmm2ext/gtkmm2ext/gtk_ui.h
+++ b/libs/gtkmm2ext/gtkmm2ext/gtk_ui.h
@@ -21,8 +21,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __pbd_gtk_ui_h__
-#define __pbd_gtk_ui_h__
+#pragma once
 
 #include <string>
 #include <map>
@@ -206,4 +205,3 @@ private:
 
 } /* namespace */
 
-#endif /* __pbd_gtk_ui_h__ */
diff --git a/libs/gtkmm2ext/gtkmm2ext/gtkutils.h b/libs/gtkmm2ext/gtkmm2ext/gtkutils.h
index a4613b7f62..e9734e520f 100644
--- a/libs/gtkmm2ext/gtkmm2ext/gtkutils.h
+++ b/libs/gtkmm2ext/gtkmm2ext/gtkutils.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __gtkutils_h__
-#define __gtkutils_h__
+#pragma once
 
 #include <string>
 
@@ -31,4 +30,3 @@ LIBGTKMM2EXT_API void gtk_set_size_request_to_display_given_text (Gtk::Widget& w
 								  const std::string& text,
 								  gint hpadding = 0,
 								  gint vpadding = 0);
-#endif /* __gtkutils_h__ */
diff --git a/libs/gtkmm2ext/gtkmm2ext/gui_thread.h b/libs/gtkmm2ext/gtkmm2ext/gui_thread.h
index f473751118..d83a55aa09 100644
--- a/libs/gtkmm2ext/gtkmm2ext/gui_thread.h
+++ b/libs/gtkmm2ext/gtkmm2ext/gui_thread.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_gtk_gui_thread_h__
-#define __ardour_gtk_gui_thread_h__
+#pragma once
 
 #include <cstdlib>
 #include <gtkmm2ext/gtk_ui.h>
@@ -33,4 +32,3 @@
 
 #define invalidator(x) PBD::EventLoop::__invalidator ((x), __FILE__, __LINE__)
 
-#endif /* __ardour_gtk_gui_thread_h__ */
diff --git a/libs/gtkmm2ext/gtkmm2ext/textviewer.h b/libs/gtkmm2ext/gtkmm2ext/textviewer.h
index ca86b91523..fa0929b07a 100644
--- a/libs/gtkmm2ext/gtkmm2ext/textviewer.h
+++ b/libs/gtkmm2ext/gtkmm2ext/textviewer.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __pbd_gtkmm_textviewer_h__
-#define __pbd_gtkmm_textviewer_h__
+#pragma once
 
 #include <string>
 
@@ -59,4 +58,3 @@ class LIBGTKMM2EXT_API TextViewer : public Gtk::Window, public Transmitter
 
 } /* namespace */
 
-#endif  // __pbd_gtkmm_textviewer_h__
diff --git a/libs/midi++2/midi++/channel.h b/libs/midi++2/midi++/channel.h
index fcdf75dc2d..dd64661c28 100644
--- a/libs/midi++2/midi++/channel.h
+++ b/libs/midi++2/midi++/channel.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __midichannel_h__
-#define __midichannel_h__
+#pragma once
 
 #include <queue>
 #include <map>
@@ -188,7 +187,6 @@ class LIBMIDIPP_API Channel : public PBD::ScopedConnectionList {
 
 } // namespace MIDI
 
-#endif // __midichannel_h__
 
 
 
diff --git a/libs/midi++2/midi++/events.h b/libs/midi++2/midi++/events.h
index 1de77b726d..51876d7682 100644
--- a/libs/midi++2/midi++/events.h
+++ b/libs/midi++2/midi++/events.h
@@ -18,8 +18,7 @@
  *
  */
 
-#ifndef __midievents_h__
-#define __midievents_h__
+#pragma once
 
 /**
  * \defgroup midi MIDI Definitions
@@ -132,4 +131,3 @@
 
 /** \} */
 
-#endif /* __midievents_h__ */
diff --git a/libs/midi++2/midi++/ipmidi_port.h b/libs/midi++2/midi++/ipmidi_port.h
index 0e5c132c07..6a330bcd32 100644
--- a/libs/midi++2/midi++/ipmidi_port.h
+++ b/libs/midi++2/midi++/ipmidi_port.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef  __libmidi_ipmidi_port_h__
-#define  __libmidi_ipmidi_port_h__
+#pragma once
 
 #include <string>
 #include <iostream>
@@ -87,4 +86,3 @@ private:
 
 } // namespace MIDI
 
-#endif // __libmidi_ipmidi_port_h__
diff --git a/libs/midi++2/midi++/libmidi_visibility.h b/libs/midi++2/midi++/libmidi_visibility.h
index 72731a0d4e..597782aec7 100644
--- a/libs/midi++2/midi++/libmidi_visibility.h
+++ b/libs/midi++2/midi++/libmidi_visibility.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libmidi_libmidi_visibility_h__
-#define __libmidi_libmidi_visibility_h__
+#pragma once
 
 #if defined(COMPILER_MSVC)
   #define LIBMIDIPP_DLL_IMPORT __declspec(dllimport)
@@ -41,4 +40,3 @@
   #define    LIBMIDIPP_LOCAL LIBMIDIPP_DLL_LOCAL
 #endif
 
-#endif /* __libmidi_libmidi_visibility_h__ */
diff --git a/libs/midi++2/midi++/mmc.h b/libs/midi++2/midi++/mmc.h
index be0b183d0a..84dc09a8b5 100644
--- a/libs/midi++2/midi++/mmc.h
+++ b/libs/midi++2/midi++/mmc.h
@@ -20,8 +20,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __midipp_mmc_h_h__
-#define __midipp_mmc_h_h__
+#pragma once
 
 #include "temporal/time.h"
 
@@ -306,4 +305,3 @@ private:
 
 } // namespace MIDI
 
-#endif /* __midipp_mmc_h_h__ */
diff --git a/libs/midi++2/midi++/parser.h b/libs/midi++2/midi++/parser.h
index e55fba28bc..cf3aa9083c 100644
--- a/libs/midi++2/midi++/parser.h
+++ b/libs/midi++2/midi++/parser.h
@@ -19,8 +19,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef  __midi_parse_h__
-#define  __midi_parse_h__
+#pragma once
 
 #include <string>
 #include <iostream>
@@ -199,5 +198,4 @@ class LIBMIDIPP_API Parser {
 
 } // namespace MIDI
 
-#endif   // __midi_parse_h__
 
diff --git a/libs/midi++2/midi++/port.h b/libs/midi++2/midi++/port.h
index 12470d358e..a6ebd1ff0f 100644
--- a/libs/midi++2/midi++/port.h
+++ b/libs/midi++2/midi++/port.h
@@ -19,8 +19,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef  __libmidi_port_base_h__
-#define  __libmidi_port_base_h__
+#pragma once
 
 #include <string>
 #include <iostream>
@@ -153,4 +152,3 @@ std::ostream & operator << (std::ostream& os, const Port& port);
 
 } // namespace MIDI
 
-#endif // __libmidi_port_base_h__
diff --git a/libs/midi++2/midi++/types.h b/libs/midi++2/midi++/types.h
index b9221b087e..81eb8ab35c 100644
--- a/libs/midi++2/midi++/types.h
+++ b/libs/midi++2/midi++/types.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __midi_types_h__
-#define __midi_types_h__
+#pragma once
 
 #include <inttypes.h>
 
@@ -91,7 +90,6 @@ namespace MIDI {
 
 } // namespace MIDI
 
-#endif // __midi_types_h__
 
 
 
diff --git a/libs/pbd/pbd/abstract_ui.h b/libs/pbd/pbd/abstract_ui.h
index cb1dc41ba8..898eda9917 100644
--- a/libs/pbd/pbd/abstract_ui.h
+++ b/libs/pbd/pbd/abstract_ui.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __pbd_abstract_ui_h__
-#define __pbd_abstract_ui_h__
+#pragma once
 
 #include <map>
 #include <string>
@@ -104,4 +103,3 @@ protected:
 
 };
 
-#endif /* __pbd_abstract_ui_h__ */
diff --git a/libs/pbd/pbd/assert.h b/libs/pbd/pbd/assert.h
index 74890638a3..72f617b0ed 100644
--- a/libs/pbd/pbd/assert.h
+++ b/libs/pbd/pbd/assert.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libpbd_assert_h__
-#define __libpbd_assert_h__
+#pragma once
 
 /*  macro designed to handle cases like this:
 
@@ -36,4 +35,3 @@
 #define x_assert(VAR, EXPR) (void) (VAR)
 # endif
 
-#endif /* __libpbd_assert_h__ */
diff --git a/libs/pbd/pbd/atomic.h b/libs/pbd/pbd/atomic.h
index 1daf66795b..19eb40c503 100644
--- a/libs/pbd/pbd/atomic.h
+++ b/libs/pbd/pbd/atomic.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libpbd_atomic_h__
-#define __libpbd_atomic_h__
+#pragma once
 
 #include <atomic>
 
@@ -31,4 +30,3 @@ void atomic_inc (std::atomic<T>& aval) { (void) aval.fetch_add (1); }
 
 }
 
-#endif /* __libpbd_atomic_h__ */
diff --git a/libs/pbd/pbd/base_ui.h b/libs/pbd/pbd/base_ui.h
index fe412f2537..23b35926f0 100644
--- a/libs/pbd/pbd/base_ui.h
+++ b/libs/pbd/pbd/base_ui.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __pbd_base_ui_h__
-#define __pbd_base_ui_h__
+#pragma once
 
 #include <string>
 #include <stdint.h>
@@ -125,4 +124,3 @@ class LIBPBD_API BaseUI : public sigc::trackable, public PBD::EventLoop
 	void main_thread ();
 };
 
-#endif /* __pbd_base_ui_h__ */
diff --git a/libs/pbd/pbd/basename.h b/libs/pbd/pbd/basename.h
index 0aa5912af6..ace910c18e 100644
--- a/libs/pbd/pbd/basename.h
+++ b/libs/pbd/pbd/basename.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libpbd_basename_h__
-#define __libpbd_basename_h__
+#pragma once
 
 #include <glibmm/ustring.h>
 
@@ -28,4 +27,3 @@ namespace PBD {
 	LIBPBD_API Glib::ustring basename_nosuffix (Glib::ustring);
 }
 
-#endif  /* __libpbd_basename_h__ */
diff --git a/libs/pbd/pbd/boost_debug.h b/libs/pbd/pbd/boost_debug.h
index 2e7796a0ad..a077b03cfc 100644
--- a/libs/pbd/pbd/boost_debug.h
+++ b/libs/pbd/pbd/boost_debug.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __pbd_boost_debug_h__
-#define __pbd_boost_debug_h__
+#pragma once
 
 #include <ostream>
 
@@ -27,4 +26,3 @@ LIBPBD_API void boost_debug_shared_ptr_mark_interesting (void* ptr, const char*
 LIBPBD_API void boost_debug_list_ptrs ();
 LIBPBD_API void boost_debug_shared_ptr_show_live_debugging (bool yn);
 
-#endif /* __pbd_boost_debug_h__ */
diff --git a/libs/pbd/pbd/cartesian.h b/libs/pbd/pbd/cartesian.h
index 26b57234ab..9a5ed20e7a 100644
--- a/libs/pbd/pbd/cartesian.h
+++ b/libs/pbd/pbd/cartesian.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libpbd_cartesian_h__
-#define __libpbd_cartesian_h__
+#pragma once
 
 #include <cfloat>
 #include <cmath>
@@ -103,4 +102,3 @@ inline void CartesianVector::angular (AngularVector& a) const {
 
 }
 
-#endif /* __libpbd_cartesian_h__ */
diff --git a/libs/pbd/pbd/command.h b/libs/pbd/pbd/command.h
index 3220081306..9e6adac09f 100644
--- a/libs/pbd/pbd/command.h
+++ b/libs/pbd/pbd/command.h
@@ -20,8 +20,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __lib_pbd_command_h__
-#define __lib_pbd_command_h__
+#pragma once
 
 #include <string>
 
@@ -61,4 +60,3 @@ protected:
 
 } /* namespace */
 
-#endif // __lib_pbd_command_h_
diff --git a/libs/pbd/pbd/configuration.h b/libs/pbd/pbd/configuration.h
index 3f67976441..a317145d93 100644
--- a/libs/pbd/pbd/configuration.h
+++ b/libs/pbd/pbd/configuration.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libpbd_configuration_h__
-#define __libpbd_configuration_h__
+#pragma once
 
 #include <map>
 #include <string>
@@ -55,4 +54,3 @@ class LIBPBD_API Configuration : public PBD::Stateful
 
 } // namespace PBD
 
-#endif /* __libpbd_configuration_h__ */
diff --git a/libs/pbd/pbd/configuration_variable.h b/libs/pbd/pbd/configuration_variable.h
index f3cbd23dbb..28c1099aa2 100644
--- a/libs/pbd/pbd/configuration_variable.h
+++ b/libs/pbd/pbd/configuration_variable.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libpbd_configuration_variable_h__
-#define __libpbd_configuration_variable_h__
+#pragma once
 
 #include <string>
 
@@ -170,4 +169,3 @@ class /*LIBPBD_API*/ ConfigVariableWithMutation<std::string> : public ConfigVari
 
 }
 
-#endif /* __libpbd_configuration_variable_h__ */
diff --git a/libs/pbd/pbd/control_math.h b/libs/pbd/pbd/control_math.h
index 9269ee1680..e6d81777e2 100644
--- a/libs/pbd/pbd/control_math.h
+++ b/libs/pbd/pbd/control_math.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __pbd_control_math_h__
-#define __pbd_control_math_h__
+#pragma once
 
 #include <assert.h>
 #include <math.h>
@@ -119,4 +118,3 @@ interpolate_gain (double f, double t, double fraction, double upper)
 	return position_to_gain (g0 + fraction * (diff)) * upper / 2.;
 }
 
-#endif
diff --git a/libs/pbd/pbd/controllable.h b/libs/pbd/pbd/controllable.h
index fe95932c8b..23b9996210 100644
--- a/libs/pbd/pbd/controllable.h
+++ b/libs/pbd/pbd/controllable.h
@@ -20,8 +20,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __pbd_controllable_h__
-#define __pbd_controllable_h__
+#pragma once
 
 #include <memory>
 #include <string>
@@ -201,4 +200,3 @@ private:
 
 }
 
-#endif /* __pbd_controllable_h__ */
diff --git a/libs/pbd/pbd/convert.h b/libs/pbd/pbd/convert.h
index aa85a10b72..632eea925a 100644
--- a/libs/pbd/pbd/convert.h
+++ b/libs/pbd/pbd/convert.h
@@ -19,8 +19,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __pbd_convert_h__
-#define __pbd_convert_h__
+#pragma once
 
 #include <stdint.h>
 #include <string>
@@ -55,4 +54,3 @@ LIBPBD_API const char* sgettext (const char *, const char *);
 
 } //namespace PBD
 
-#endif /* __pbd_convert_h__ */
diff --git a/libs/pbd/pbd/cpus.h b/libs/pbd/pbd/cpus.h
index 2fca0fe99c..19b6dc646c 100644
--- a/libs/pbd/pbd/cpus.h
+++ b/libs/pbd/pbd/cpus.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libpbd_cpus_h__
-#define __libpbd_cpus_h__
+#pragma once
 
 #include <stdint.h>
 
@@ -25,4 +24,3 @@
 
 LIBPBD_API extern uint32_t hardware_concurrency ();
 
-#endif /* __libpbd_cpus_h__ */
diff --git a/libs/pbd/pbd/crossthread.h b/libs/pbd/pbd/crossthread.h
index 45e841fe87..08f61a5b58 100644
--- a/libs/pbd/pbd/crossthread.h
+++ b/libs/pbd/pbd/crossthread.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __pbd__crossthread_h__
-#define __pbd__crossthread_h__
+#pragma once
 
 #ifdef check
 #undef check
@@ -105,4 +104,3 @@ private:
 
 };
 
-#endif /* __pbd__crossthread_h__ */
diff --git a/libs/pbd/pbd/debug.h b/libs/pbd/pbd/debug.h
index b62f450150..7efea83d11 100644
--- a/libs/pbd/pbd/debug.h
+++ b/libs/pbd/pbd/debug.h
@@ -19,8 +19,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libpbd_debug_h__
-#define __libpbd_debug_h__
+#pragma once
 
 #include <bitset>
 #include <stdint.h>
@@ -117,5 +116,4 @@ namespace PBD {
 #define DEBUG_RESULT_CAST(type,var,cast_expr,...) __VA_ARGS__
 #define DEBUG_ASSIGN(var,expr)
 #endif
-#endif /* __libpbd_debug_h__ */
 
diff --git a/libs/pbd/pbd/debug_rt_alloc.h b/libs/pbd/pbd/debug_rt_alloc.h
index c2841a6139..184377e962 100644
--- a/libs/pbd/pbd/debug_rt_alloc.h
+++ b/libs/pbd/pbd/debug_rt_alloc.h
@@ -18,8 +18,7 @@
 
 #ifdef DEBUG_RT_ALLOC
 
-#ifndef __pbd_debug_rt_alloc_h__
-#define __pbd_debug_rt_alloc_h__
+#pragma once
 
 #include "pbd/libpbd_visibility.h"
 
@@ -38,8 +37,6 @@ LIBPBD_API extern void resume_rt_malloc_checks ();
 
 }
 
-#endif
-
 #else
 
 #define suspend_rt_malloc_checks() {}
diff --git a/libs/pbd/pbd/demangle.h b/libs/pbd/pbd/demangle.h
index d1c4814969..2be51e1a6f 100644
--- a/libs/pbd/pbd/demangle.h
+++ b/libs/pbd/pbd/demangle.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libpbd_demangle_h__
-#define __libpbd_demangle_h__
+#pragma once
 
 #include <string>
 #include <cstdlib>
@@ -50,4 +49,3 @@ std::string demangled_name(T const& obj)
 
 } // namespace
 
-#endif // __libpbd_demangle_h__
diff --git a/libs/pbd/pbd/destructible.h b/libs/pbd/pbd/destructible.h
index 804f32fedc..d58db24b72 100644
--- a/libs/pbd/pbd/destructible.h
+++ b/libs/pbd/pbd/destructible.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __pbd_destructible_h__
-#define __pbd_destructible_h__
+#pragma once
 
 #include "pbd/signals.h"
 #include "pbd/libpbd_visibility.h"
@@ -36,4 +35,3 @@ public:
 
 }
 
-#endif /* __pbd_destructible_h__ */
diff --git a/libs/pbd/pbd/downloader.h b/libs/pbd/pbd/downloader.h
index 48002896c9..ebdfa95cb7 100644
--- a/libs/pbd/pbd/downloader.h
+++ b/libs/pbd/pbd/downloader.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libpbd_downloader_h__
-#define __libpbd_downloader_h__
+#pragma once
 
 #include <atomic>
 #include <string>
@@ -66,4 +65,3 @@ class LIBPBD_API Downloader {
 
 } /* namespace */
 
-#endif
diff --git a/libs/pbd/pbd/enumwriter.h b/libs/pbd/pbd/enumwriter.h
index abacbb16ac..fc62c822af 100644
--- a/libs/pbd/pbd/enumwriter.h
+++ b/libs/pbd/pbd/enumwriter.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __pbd_enumwriter_h__
-#define __pbd_enumwriter_h__
+#pragma once
 
 #include <map>
 #include <string>
@@ -97,4 +96,3 @@ class LIBPBD_API EnumWriter {
 #define enum_2_string(e) (PBD::EnumWriter::instance().write (typeid(e).name(), e))
 #define string_2_enum(str,e) (PBD::EnumWriter::instance().read (typeid(e).name(), (str)))
 
-#endif /*  __pbd_enumwriter_h__ */
diff --git a/libs/pbd/pbd/epa.h b/libs/pbd/pbd/epa.h
index 5f22770e3b..4fe6d14d62 100644
--- a/libs/pbd/pbd/epa.h
+++ b/libs/pbd/pbd/epa.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libpbd_epa_h__
-#define __libpbd_epa_h__
+#pragma once
 
 #include <map>
 #include <string>
@@ -49,4 +48,3 @@ class LIBPBD_API EnvironmentalProtectionAgency {
 
 }
 
-#endif /* __libpbd_epa_h__ */
diff --git a/libs/pbd/pbd/error.h b/libs/pbd/pbd/error.h
index ba4b301baf..0f2eeb56a3 100644
--- a/libs/pbd/pbd/error.h
+++ b/libs/pbd/pbd/error.h
@@ -15,8 +15,7 @@
  * with this program; if not, write to the Free Software Foundation, Inc.,
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
-#ifndef __libpbd_error_h__
-#define __libpbd_error_h__
+#pragma once
 
 #include "pbd/libpbd_visibility.h"
 #include "transmitter.h"
@@ -29,4 +28,3 @@ namespace PBD {
 	LIBPBD_API extern Transmitter fatal;
 }
 
-#endif  // __libpbd_error_h__
diff --git a/libs/pbd/pbd/event_loop.h b/libs/pbd/pbd/event_loop.h
index 48df8620df..baf5a21ec7 100644
--- a/libs/pbd/pbd/event_loop.h
+++ b/libs/pbd/pbd/event_loop.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __pbd_event_loop_h__
-#define __pbd_event_loop_h__
+#pragma once
 
 #include <atomic>
 #include <string>
@@ -140,4 +139,3 @@ private:
 
 #define MISSING_INVALIDATOR nullptr // used to mark places where we fail to provide an invalidator
 
-#endif /* __pbd_event_loop_h__ */
diff --git a/libs/pbd/pbd/failed_constructor.h b/libs/pbd/pbd/failed_constructor.h
index 2e89cf8edf..984bee6c17 100644
--- a/libs/pbd/pbd/failed_constructor.h
+++ b/libs/pbd/pbd/failed_constructor.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __pbd_failed_constructor_h__
-#define __pbd_failed_constructor_h__
+#pragma once
 
 #include <exception>
 
@@ -28,4 +27,3 @@ class LIBPBD_API failed_constructor : public std::exception {
 	virtual const char *what() const throw() { return "failed constructor"; }
 };
 
-#endif /* __pbd_failed_constructor_h__ */
diff --git a/libs/pbd/pbd/fastlog.h b/libs/pbd/pbd/fastlog.h
index 57de7db8e2..0c118a1f2b 100644
--- a/libs/pbd/pbd/fastlog.h
+++ b/libs/pbd/pbd/fastlog.h
@@ -5,8 +5,7 @@
  * terms of the Do What The Fuck You Want To Public License, Version 2,
  * as published by Sam Hocevar. See http://www.wtfpl.net/ for more details.
  */
-#ifndef __pbd_fastlog_h__
-#define __pbd_fastlog_h__
+#pragma once
 
 #include <math.h> /* for HUGE_VAL */
 
@@ -45,4 +44,3 @@ static inline float fast_log10 (const float val)
 
 static inline float minus_infinity(void) { return -HUGE_VAL; }
 
-#endif /* __pbd_fastlog_h__ */
diff --git a/libs/pbd/pbd/ffs.h b/libs/pbd/pbd/ffs.h
index 73fc2b5c30..51f82705b8 100644
--- a/libs/pbd/pbd/ffs.h
+++ b/libs/pbd/pbd/ffs.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libpbd_ffs_h__
-#define __libpbd_ffs_h__
+#pragma once
 
 #include "pbd/libpbd_visibility.h"
 
@@ -27,4 +26,3 @@ namespace PBD {
 	LIBPBD_API int ffs(int x);
 }
 
-#endif  /* __libpbd_ffs_h__ */
diff --git a/libs/pbd/pbd/floating.h b/libs/pbd/pbd/floating.h
index 3d1705189a..3dd01a8f2b 100644
--- a/libs/pbd/pbd/floating.h
+++ b/libs/pbd/pbd/floating.h
@@ -23,8 +23,7 @@
  * Code assumed to be in the public domain.
  */
 
-#ifndef __libpbd__floating_h__
-#define __libpbd__floating_h__
+#pragma once
 
 #include <stdint.h>
 
@@ -76,4 +75,3 @@ static inline bool floateq (float a, float b, int max_ulps_diff)
 
 } /* namespace */
 
-#endif /* __libpbd__floating_h__ */
diff --git a/libs/pbd/pbd/fpu.h b/libs/pbd/pbd/fpu.h
index 9dfd68a27a..2859a9a4f0 100644
--- a/libs/pbd/pbd/fpu.h
+++ b/libs/pbd/pbd/fpu.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __pbd_fpu_h__
-#define __pbd_fpu_h__
+#pragma once
 
 #include "pbd/libpbd_visibility.h"
 
@@ -62,4 +61,3 @@ class LIBPBD_API FPU {
 
 }
 
-#endif /* __pbd_fpu_h__ */
diff --git a/libs/pbd/pbd/functor_command.h b/libs/pbd/pbd/functor_command.h
index 533e8d207f..e00bd8a5f8 100644
--- a/libs/pbd/pbd/functor_command.h
+++ b/libs/pbd/pbd/functor_command.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __lib_pbd_functor_command_h__
-#define __lib_pbd_functor_command_h__
+#pragma once
 
 #include <iostream>
 #include <sstream>
@@ -114,5 +113,4 @@ FunctorCommand<obj_type, arg_type>::functor_map;
 
 };
 
-#endif // __lib_pbd_functor_command_h__
 
diff --git a/libs/pbd/pbd/glib_event_source.h b/libs/pbd/pbd/glib_event_source.h
index e5377ab6ad..bbd097cc9d 100644
--- a/libs/pbd/pbd/glib_event_source.h
+++ b/libs/pbd/pbd/glib_event_source.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libpbd_glib_event_source_h__
-#define __libpbd_glib_event_source_h__
+#pragma once
 
 #include <boost/function.hpp>
 
@@ -47,4 +46,3 @@ class LIBPBD_API GlibEventLoopCallback
 	boost::function<void()> _callback;
 };
 
-#endif /* __libpbd_glib_event_source_h__ */
diff --git a/libs/pbd/pbd/gstdio_compat.h b/libs/pbd/pbd/gstdio_compat.h
index 5102cf67c6..597587d833 100644
--- a/libs/pbd/pbd/gstdio_compat.h
+++ b/libs/pbd/pbd/gstdio_compat.h
@@ -23,8 +23,7 @@
  * https://tracker.ardour.org/view.php?id=6575
  */
 
-#ifndef __pbd_gstdio_compat_h__
-#define __pbd_gstdio_compat_h__
+#pragma once
 
 #include <glib/gstdio.h>
 
@@ -86,4 +85,3 @@ pbd_g_stat(const gchar* filename, GStatBufW64* buf)
 #  define g_lstat pbd_g_stat
 #endif
 
-#endif /* __pbd_gstdio_compat_h__ */
diff --git a/libs/pbd/pbd/history_owner.h b/libs/pbd/pbd/history_owner.h
index cdc910548d..a1d039b722 100644
--- a/libs/pbd/pbd/history_owner.h
+++ b/libs/pbd/pbd/history_owner.h
@@ -1,5 +1,4 @@
-#ifndef __libpbd_history_owner_h__
-#define __libpbd_history_owner_h__
+#pragma once
 
 #include <string>
 #include <vector>
@@ -101,4 +100,3 @@ class LIBPBD_API HistoryOwner
 
 } /* namespace PBD */
 
-#endif /* __libpbd_history_owner_h__ */
diff --git a/libs/pbd/pbd/id.h b/libs/pbd/pbd/id.h
index 7d2519d6c3..cf8d571e51 100644
--- a/libs/pbd/pbd/id.h
+++ b/libs/pbd/pbd/id.h
@@ -19,8 +19,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __pbd_id_h__
-#define __pbd_id_h__
+#pragma once
 
 #include <stdint.h>
 #include <string>
@@ -79,4 +78,3 @@ class LIBPBD_API ID {
 
 LIBPBD_API std::ostream& operator<< (std::ostream& ostr, const PBD::ID&);
 
-#endif /* __pbd_id_h__ */
diff --git a/libs/pbd/pbd/inflater.h b/libs/pbd/pbd/inflater.h
index 55669e6231..22e9579124 100644
--- a/libs/pbd/pbd/inflater.h
+++ b/libs/pbd/pbd/inflater.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libpbd_inflater_h__
-#define __libpbd_inflater_h__
+#pragma once
 
 #include <string>
 
@@ -56,4 +55,3 @@ private:
 
 } /* namespace */
 
-#endif 
diff --git a/libs/pbd/pbd/integer_division.h b/libs/pbd/pbd/integer_division.h
index 0979f1cf7e..0367c5e45f 100644
--- a/libs/pbd/pbd/integer_division.h
+++ b/libs/pbd/pbd/integer_division.h
@@ -16,8 +16,7 @@
     Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */
 
-#ifndef __libpbd_integer_division_h__
-#define __libpbd_integer_division_h__
+#pragma once
 
 #include <cstdint>
 
@@ -122,4 +121,3 @@ int64_t muldiv_floor (int64_t v, int64_t n, int64_t d)
 }
 } /* namespace */
 
-#endif /* __libpbd_integer_division_h___ */
diff --git a/libs/pbd/pbd/libpbd_visibility.h b/libs/pbd/pbd/libpbd_visibility.h
index f18f4683e5..9a5fc7f585 100644
--- a/libs/pbd/pbd/libpbd_visibility.h
+++ b/libs/pbd/pbd/libpbd_visibility.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libpbd_libpbd_visibility_h__
-#define __libpbd_libpbd_visibility_h__
+#pragma once
 
 #if defined(COMPILER_MSVC)
   #define LIBPBD_DLL_IMPORT __declspec(dllimport)
@@ -55,4 +54,3 @@
   #define LIBPBD_LOCAL LIBPBD_DLL_LOCAL
 #endif
 
-#endif /* __libpbd_libpbd_visibility_h__ */
diff --git a/libs/pbd/pbd/malign.h b/libs/pbd/pbd/malign.h
index 386df7e7ed..76b2afa4af 100644
--- a/libs/pbd/pbd/malign.h
+++ b/libs/pbd/pbd/malign.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __pbd_malign_h__
-#define __pbd_malign_h__
+#pragma once
 
 #include <stdlib.h>
 
@@ -29,4 +28,3 @@ LIBPBD_API void cache_aligned_free (void* memptr);
 LIBPBD_API int  aligned_malloc (void** memptr, size_t size, size_t alignment);
 LIBPBD_API void aligned_free (void* memptr);
 
-#endif /* __pbd_malign_h__ */
diff --git a/libs/pbd/pbd/match.h b/libs/pbd/pbd/match.h
index 33d0c5d283..eeccc2ac11 100644
--- a/libs/pbd/pbd/match.h
+++ b/libs/pbd/pbd/match.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libpbd_match_h__
-#define __libpbd_match_h__
+#pragma once
 
 #include <string>
 #include <boost/tokenizer.hpp>
@@ -41,4 +40,3 @@ match_search_strings (std::string const& haystack, std::string const& needle)
 
 }
 
-#endif /* __libpbd_match_h__ */
diff --git a/libs/pbd/pbd/mathfix.h b/libs/pbd/pbd/mathfix.h
index 01feb520f7..f6f022848a 100644
--- a/libs/pbd/pbd/mathfix.h
+++ b/libs/pbd/pbd/mathfix.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __pbd_mathfix_h__
-#define __pbd_mathfix_h__
+#pragma once
 
 /* this is necessary to support older releases of OSX where
    they moved around some of the standard math functions
@@ -29,4 +28,3 @@
 #endif
 
 
-#endif
diff --git a/libs/pbd/pbd/memento_command.h b/libs/pbd/pbd/memento_command.h
index ec570d99b7..e9eb1fa3d0 100644
--- a/libs/pbd/pbd/memento_command.h
+++ b/libs/pbd/pbd/memento_command.h
@@ -20,8 +20,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __lib_pbd_memento_command_h__
-#define __lib_pbd_memento_command_h__
+#pragma once
 
 #include <iostream>
 
@@ -174,4 +173,3 @@ protected:
 	PBD::ScopedConnection _binder_death_connection;
 };
 
-#endif // __lib_pbd_memento_h__
diff --git a/libs/pbd/pbd/microseconds.h b/libs/pbd/pbd/microseconds.h
index b4abce60bf..6eb2797f7f 100644
--- a/libs/pbd/pbd/microseconds.h
+++ b/libs/pbd/pbd/microseconds.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libpbd_microseconds_h__
-#define __libpbd_microseconds_h__
+#pragma once
 
 #include <inttypes.h>
 
@@ -31,4 +30,3 @@ namespace PBD {
 	void microsecond_timer_init ();
 }
 
-#endif /* __libpbd_microseconds_h__ */
diff --git a/libs/pbd/pbd/mountpoint.h b/libs/pbd/pbd/mountpoint.h
index 0bdc848324..220e8b76c5 100644
--- a/libs/pbd/pbd/mountpoint.h
+++ b/libs/pbd/pbd/mountpoint.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __pbd_mountpoint_h__
-#define __pbd_mountpoint_h__
+#pragma once
 
 #include <string>
 
@@ -25,4 +24,3 @@
 
 LIBPBD_API std::string mountpoint (std::string path);
 
-#endif // __pbd_mountpoint_h__
diff --git a/libs/pbd/pbd/openuri.h b/libs/pbd/pbd/openuri.h
index 1edf987f53..ff43604c5d 100644
--- a/libs/pbd/pbd/openuri.h
+++ b/libs/pbd/pbd/openuri.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libpbd_openuri_h__
-#define __libpbd_openuri_h__
+#pragma once
 
 #include <string>
 
@@ -29,4 +28,3 @@ namespace PBD {
         LIBPBD_API bool open_folder (const std::string&);
 }
 
-#endif
diff --git a/libs/pbd/pbd/pathexpand.h b/libs/pbd/pbd/pathexpand.h
index 95c158efd0..a617d1eaef 100644
--- a/libs/pbd/pbd/pathexpand.h
+++ b/libs/pbd/pbd/pathexpand.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libpbd_path_expand_h__
-#define __libpbd_path_expand_h__
+#pragma once
 
 #include <string>
 #include <vector>
@@ -31,5 +30,4 @@ namespace PBD {
 	LIBPBD_API std::vector<std::string> parse_path(std::string path, bool check_if_exists = false);
 }
 
-#endif /* __libpbd_path_expand_h__ */
 
diff --git a/libs/pbd/pbd/pbd.h b/libs/pbd/pbd/pbd.h
index e6aeec899c..fdf38fa35e 100644
--- a/libs/pbd/pbd/pbd.h
+++ b/libs/pbd/pbd/pbd.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libpbd_pbd_h__
-#define __libpbd_pbd_h__
+#pragma once
 
 #include "pbd/libpbd_visibility.h"
 
@@ -29,4 +28,3 @@ namespace PBD {
 
 } // namespace PBD
 
-#endif
diff --git a/libs/pbd/pbd/playback_buffer.h b/libs/pbd/pbd/playback_buffer.h
index d7045b66f2..9bbaa73a2e 100644
--- a/libs/pbd/pbd/playback_buffer.h
+++ b/libs/pbd/pbd/playback_buffer.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef playback_buffer_h
-#define playback_buffer_h
+#pragma once
 
 #include <atomic>
 #include <cstdint>
@@ -334,4 +333,3 @@ PlaybackBuffer<T>::read (T *dest, size_t cnt, bool commit, size_t offset)
 
 } /* end namespace */
 
-#endif /* __ringbuffer_h__ */
diff --git a/libs/pbd/pbd/pool.h b/libs/pbd/pbd/pool.h
index 1d21b1942c..0346736b50 100644
--- a/libs/pbd/pbd/pool.h
+++ b/libs/pbd/pbd/pool.h
@@ -19,8 +19,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __qm_pool_h__
-#define __qm_pool_h__
+#pragma once
 
 #include <string>
 #include <vector>
@@ -175,4 +174,3 @@ private:
 
 } // namespace PBD
 
-#endif // __qm_pool_h__
diff --git a/libs/pbd/pbd/properties.h b/libs/pbd/pbd/properties.h
index 8ee2ab0c3b..d1d6ce9c46 100644
--- a/libs/pbd/pbd/properties.h
+++ b/libs/pbd/pbd/properties.h
@@ -20,8 +20,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __pbd_properties_h__
-#define __pbd_properties_h__
+#pragma once
 
 #include <string>
 #include <list>
@@ -481,4 +480,3 @@ private:
 #include "pbd/property_list_impl.h"
 #include "pbd/property_basics_impl.h"
 
-#endif /* __pbd_properties_h__ */
diff --git a/libs/pbd/pbd/property_basics.h b/libs/pbd/pbd/property_basics.h
index 3ca45e946e..b5f9f14aff 100644
--- a/libs/pbd/pbd/property_basics.h
+++ b/libs/pbd/pbd/property_basics.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libpbd_property_basics_h__
-#define __libpbd_property_basics_h__
+#pragma once
 
 #include <glib.h>
 #include <set>
@@ -177,4 +176,3 @@ namespace std {
 ostream& operator<< (std::ostream& os, PBD::PropertyChange const & pc);
 }
 
-#endif /* __libpbd_property_basics_h__ */
diff --git a/libs/pbd/pbd/property_basics_impl.h b/libs/pbd/pbd/property_basics_impl.h
index 2000ec68cb..5881b13d61 100644
--- a/libs/pbd/pbd/property_basics_impl.h
+++ b/libs/pbd/pbd/property_basics_impl.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libpbd_property_basics_impl_h__
-#define __libpbd_property_basics_impl_h__
+#pragma once
 
 namespace PBD {
 
@@ -49,4 +48,3 @@ PropertyChange::add (PropertyDescriptor<T> p)
 
 }
 
-#endif /* __libpbd_property_basics_impl_h__ */
diff --git a/libs/pbd/pbd/property_list.h b/libs/pbd/pbd/property_list.h
index 330345853f..83a65efa38 100644
--- a/libs/pbd/pbd/property_list.h
+++ b/libs/pbd/pbd/property_list.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __pbd_property_list_h__
-#define __pbd_property_list_h__
+#pragma once
 
 #include <map>
 
@@ -87,4 +86,3 @@ public:
 
 }
 
-#endif /* __pbd_property_list_h__ */
diff --git a/libs/pbd/pbd/property_list_impl.h b/libs/pbd/pbd/property_list_impl.h
index b99f07236b..9db0c40677 100644
--- a/libs/pbd/pbd/property_list_impl.h
+++ b/libs/pbd/pbd/property_list_impl.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libpbd_property_list_impl_h__
-#define __libpbd_property_list_impl_h__
+#pragma once
 
 #include "pbd/property_list.h"
 #include "pbd/properties.h"
@@ -39,4 +38,3 @@ PropertyList::remove (PropertyDescriptor<T> pid) {
 
 }
 
-#endif /* __libpbd_property_list_impl_h__ */
diff --git a/libs/pbd/pbd/rcu.h b/libs/pbd/pbd/rcu.h
index 3f84425c0c..8f86ba6357 100644
--- a/libs/pbd/pbd/rcu.h
+++ b/libs/pbd/pbd/rcu.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __pbd_rcu_h__
-#define __pbd_rcu_h__
+#pragma once
 
 #include <atomic>
 #include <mutex>
@@ -337,4 +336,3 @@ private:
 	std::shared_ptr<T> _copy;
 };
 
-#endif /* __pbd_rcu_h__ */
diff --git a/libs/pbd/pbd/receiver.h b/libs/pbd/pbd/receiver.h
index 94264e51c9..fbbae11643 100644
--- a/libs/pbd/pbd/receiver.h
+++ b/libs/pbd/pbd/receiver.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libmisc_receiver_h__
-#define __libmisc_receiver_h__
+#pragma once
 
 #include <vector>
 
@@ -44,4 +43,3 @@ class LIBPBD_API Receiver : public sigc::trackable
 	PBD::ScopedConnectionList connections;
 };
 
-#endif  // __libmisc_receiver_h__
diff --git a/libs/pbd/pbd/replace_all.h b/libs/pbd/pbd/replace_all.h
index 9308bf80dd..66d92d12fe 100644
--- a/libs/pbd/pbd/replace_all.h
+++ b/libs/pbd/pbd/replace_all.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __pbd_replace_all_h__
-#define __pbd_replace_all_h__
+#pragma once
 
 #include <string>
 
@@ -26,4 +25,3 @@
 LIBPBD_API int replace_all (std::string& str, const std::string& target, const std::string& replacement);
 LIBPBD_API std::string poor_mans_glob (std::string path);
 
-#endif // __pbd_replace_all_h__
diff --git a/libs/pbd/pbd/ringbuffer.h b/libs/pbd/pbd/ringbuffer.h
index 0fa5798e02..58f166ccd9 100644
--- a/libs/pbd/pbd/ringbuffer.h
+++ b/libs/pbd/pbd/ringbuffer.h
@@ -20,8 +20,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef ringbuffer_h
-#define ringbuffer_h
+#pragma once
 
 #include <atomic>
 #include <cstring>
@@ -291,4 +290,3 @@ RingBuffer<T>::get_write_vector (typename RingBuffer<T>::rw_vector *vec)
 
 } /* end namespace */
 
-#endif /* __ringbuffer_h__ */
diff --git a/libs/pbd/pbd/ringbufferNPT.h b/libs/pbd/pbd/ringbufferNPT.h
index 6f3b5045d6..6d73587704 100644
--- a/libs/pbd/pbd/ringbufferNPT.h
+++ b/libs/pbd/pbd/ringbufferNPT.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef ringbuffer_npt_h
-#define ringbuffer_npt_h
+#pragma once
 
 //#include <sys/mman.h>
 
@@ -290,4 +289,3 @@ RingBufferNPT<T>::get_write_vector (typename RingBufferNPT<T>::rw_vector *vec)
 
 } /* namespace */
 
-#endif /* __ringbuffer_npt_h__ */
diff --git a/libs/pbd/pbd/scoped_file_descriptor.h b/libs/pbd/pbd/scoped_file_descriptor.h
index 1a6540ff04..06c53d15fe 100644
--- a/libs/pbd/pbd/scoped_file_descriptor.h
+++ b/libs/pbd/pbd/scoped_file_descriptor.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libpbd_scoped_file_descriptor_h__
-#define __libpbd_scoped_file_descriptor_h__
+#pragma once
 
 namespace PBD {
 
@@ -30,4 +29,3 @@ struct ScopedFileDescriptor {
 
 }
 
-#endif /* __libpbd_scoped_file_descriptor_h__ */
diff --git a/libs/pbd/pbd/search_path.h b/libs/pbd/pbd/search_path.h
index 1b26adffb7..15e90eed16 100644
--- a/libs/pbd/pbd/search_path.h
+++ b/libs/pbd/pbd/search_path.h
@@ -21,8 +21,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libpbd_search_path_h__
-#define __libpbd_search_path_h__
+#pragma once
 
 #include <string>
 #include <vector>
@@ -149,4 +148,3 @@ LIBPBD_API void export_search_path (const std::string& base_dir, const char* var
 
 } // namespace PBD
 
-#endif /* __libpbd_search_path_h__ */
diff --git a/libs/pbd/pbd/selectable.h b/libs/pbd/pbd/selectable.h
index 492de0b4f7..04bec40b28 100644
--- a/libs/pbd/pbd/selectable.h
+++ b/libs/pbd/pbd/selectable.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __selectable_h__
-#define __selectable_h__
+#pragma once
 
 #include <list>
 #include <string>
@@ -99,4 +98,3 @@ class LIBPBD_API Selector {
 } /* namespace */
 
 
-#endif // __selectable_h__
diff --git a/libs/pbd/pbd/semutils.h b/libs/pbd/pbd/semutils.h
index bdc47072d2..74b273b456 100644
--- a/libs/pbd/pbd/semutils.h
+++ b/libs/pbd/pbd/semutils.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __pbd_semutils_h__
-#define __pbd_semutils_h__
+#pragma once
 
 #if (defined PLATFORM_WINDOWS && !defined USE_PTW32_SEMAPHORE)
 #define WINDOWS_SEMAPHORE 1
@@ -73,4 +72,3 @@ class LIBPBD_API Semaphore {
 
 }
 
-#endif /* __pbd_semutils_h__ */
diff --git a/libs/pbd/pbd/sequence_property.h b/libs/pbd/pbd/sequence_property.h
index bdc4d70cc2..94ae1f3bba 100644
--- a/libs/pbd/pbd/sequence_property.h
+++ b/libs/pbd/pbd/sequence_property.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libpbd_sequence_property_h__
-#define __libpbd_sequence_property_h__
+#pragma once
 
 #include <iostream>
 
@@ -368,4 +367,3 @@ private:
 
 }
 
-#endif /* __libpbd_sequence_property_h__ */
diff --git a/libs/pbd/pbd/shortpath.h b/libs/pbd/pbd/shortpath.h
index 91b1e4b9d8..bf926014bc 100644
--- a/libs/pbd/pbd/shortpath.h
+++ b/libs/pbd/pbd/shortpath.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __pbd_shortpath_h__
-#define __pbd_shortpath_h__
+#pragma once
 
 #include <glibmm/ustring.h>
 
@@ -25,4 +24,3 @@
 
 LIBPBD_API Glib::ustring short_path (const Glib::ustring& path, Glib::ustring::size_type target_characters);
 
-#endif /* __pbd_shortpath_h__ */
diff --git a/libs/pbd/pbd/signals.h b/libs/pbd/pbd/signals.h
index ea1a779879..b9d8e3a4aa 100644
--- a/libs/pbd/pbd/signals.h
+++ b/libs/pbd/pbd/signals.h
@@ -19,8 +19,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __pbd_signals_h__
-#define __pbd_signals_h__
+#pragma once
 
 #include <csignal>
 
@@ -227,4 +226,3 @@ class LIBPBD_API ScopedConnectionList  : public boost::noncopyable
 
 } /* namespace */
 
-#endif /* __pbd_signals_h__ */
diff --git a/libs/pbd/pbd/stacktrace.h b/libs/pbd/pbd/stacktrace.h
index daf61e88c1..94afb60636 100644
--- a/libs/pbd/pbd/stacktrace.h
+++ b/libs/pbd/pbd/stacktrace.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libpbd_stacktrace_h__
-#define __libpbd_stacktrace_h__
+#pragma once
 
 #ifdef HAVE_WAFBUILD
 #include "libpbd-config.h"
@@ -119,4 +118,3 @@ template<typename T> /*LIBPBD_API*/ Glib::Threads::Mutex PBD::thing_with_backtra
 
 } // namespace PBD
 
-#endif /* __libpbd_stacktrace_h__ */
diff --git a/libs/pbd/pbd/stateful.h b/libs/pbd/pbd/stateful.h
index 8fd259abc8..9d10079759 100644
--- a/libs/pbd/pbd/stateful.h
+++ b/libs/pbd/pbd/stateful.h
@@ -20,8 +20,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __pbd_stateful_h__
-#define __pbd_stateful_h__
+#pragma once
 
 #include <atomic>
 #include <string>
@@ -149,4 +148,3 @@ class LIBPBD_API Stateful {
 
 } // namespace PBD
 
-#endif /* __pbd_stateful_h__ */
diff --git a/libs/pbd/pbd/stateful_diff_command.h b/libs/pbd/pbd/stateful_diff_command.h
index 6973d52b65..60d986ddff 100644
--- a/libs/pbd/pbd/stateful_diff_command.h
+++ b/libs/pbd/pbd/stateful_diff_command.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __pbd_stateful_diff_command_h__
-#define __pbd_stateful_diff_command_h__
+#pragma once
 
 #include <memory>
 
@@ -54,4 +53,3 @@ private:
 
 }; // namespace PBD
 
-#endif /* __pbd_stateful_diff_command_h__ */
diff --git a/libs/pbd/pbd/statefuldestructible.h b/libs/pbd/pbd/statefuldestructible.h
index 3881aff97a..b9aa4503ed 100644
--- a/libs/pbd/pbd/statefuldestructible.h
+++ b/libs/pbd/pbd/statefuldestructible.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __pbd_stateful_destructible_h__
-#define __pbd_stateful_destructible_h__
+#pragma once
 
 #include "pbd/libpbd_visibility.h"
 #include "pbd/stateful.h"
@@ -32,4 +31,3 @@ class LIBPBD_API StatefulDestructible : virtual public Stateful, virtual public
 
 }
 
-#endif /* __pbd_stateful_destructible_h__ */
diff --git a/libs/pbd/pbd/stl_delete.h b/libs/pbd/pbd/stl_delete.h
index 8d5d6c4ab2..8f16acd611 100644
--- a/libs/pbd/pbd/stl_delete.h
+++ b/libs/pbd/pbd/stl_delete.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libmisc_stl_delete_h__
-#define __libmisc_stl_delete_h__
+#pragma once
 
 #include "pbd/libpbd_visibility.h"
 
@@ -86,4 +85,3 @@ template<class T> void /*LIBPBD_API*/ set_delete (std::set<T *> *sset)
 }
 #endif // _CPP_SET || _GLIBCXX_SET || __SGI_STL_SET
 
-#endif // __libmisc_stl_delete_h__
diff --git a/libs/pbd/pbd/strsplit.h b/libs/pbd/pbd/strsplit.h
index d6b20979da..0b459a08e6 100644
--- a/libs/pbd/pbd/strsplit.h
+++ b/libs/pbd/pbd/strsplit.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __pbd_strplit_h__
-#define __pbd_strplit_h__
+#pragma once
 
 #include <string>
 #include <vector>
@@ -28,4 +27,3 @@
 LIBPBD_API extern void split (std::string, std::vector<std::string>&, char);
 LIBPBD_API extern void split (Glib::ustring, std::vector<Glib::ustring>&, char);
 
-#endif // __pbd_strplit_h__
diff --git a/libs/pbd/pbd/textreceiver.h b/libs/pbd/pbd/textreceiver.h
index 86bf7ad5f0..be1ffe9f5e 100644
--- a/libs/pbd/pbd/textreceiver.h
+++ b/libs/pbd/pbd/textreceiver.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libmisc_textreceiver_h__
-#define __libmisc_textreceiver_h__
+#pragma once
 
 #include <string>
 
@@ -36,4 +35,3 @@ class LIBPBD_API TextReceiver : public Receiver
 	std::string name;
 };
 
-#endif //__libmisc_textreceiver_h__
diff --git a/libs/pbd/pbd/thrown_error.h b/libs/pbd/pbd/thrown_error.h
index 0ad5d30719..c91c4b3d1c 100644
--- a/libs/pbd/pbd/thrown_error.h
+++ b/libs/pbd/pbd/thrown_error.h
@@ -15,8 +15,7 @@
  * with this program; if not, write to the Free Software Foundation, Inc.,
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
-#ifndef __qm_thrown_error_h__
-#define __qm_thrown_error_h__
+#pragma once
 
 #include "pbd/libpbd_visibility.h"
 #include "transmitter.h"
@@ -33,6 +32,5 @@ class LIBPBD_API ThrownError : public Transmitter {
 	virtual void deliver () = 0;
 };
 
-#endif // __qm_thrown_error_h__
 
 
diff --git a/libs/pbd/pbd/timer.h b/libs/pbd/pbd/timer.h
index 7970b47a8f..6c95da2537 100644
--- a/libs/pbd/pbd/timer.h
+++ b/libs/pbd/pbd/timer.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libpbd_timer_h__
-#define __libpbd_timer_h__
+#pragma once
 
 #include <sigc++/signal.h>
 
@@ -125,4 +124,3 @@ protected:
 
 } // namespace PBD
 
-#endif // __libpbd_timer_h__
diff --git a/libs/pbd/pbd/timing.h b/libs/pbd/pbd/timing.h
index 31259ab157..26dbce3194 100644
--- a/libs/pbd/pbd/timing.h
+++ b/libs/pbd/pbd/timing.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libpbd_timing_h__
-#define __libpbd_timing_h__
+#pragma once
 
 #include <glib.h>
 
@@ -323,4 +322,3 @@ private:
 
 } // namespace PBD
 
-#endif // __libpbd_timing_h__
diff --git a/libs/pbd/pbd/touchable.h b/libs/pbd/pbd/touchable.h
index a50ad2eda9..feb895cb4d 100644
--- a/libs/pbd/pbd/touchable.h
+++ b/libs/pbd/pbd/touchable.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __pbd_touchable_h__
-#define __pbd_touchable_h__
+#pragma once
 
 #include "pbd/libpbd_visibility.h"
 
@@ -87,4 +86,3 @@ class /*LIBPBD_API*/ DynamicTouchable2 : public Touchable
 	T3 arg2;
 };
 
-#endif // __pbd_touchable_h__
diff --git a/libs/pbd/pbd/transmitter.h b/libs/pbd/pbd/transmitter.h
index 7d189914ce..47ee6daa3a 100644
--- a/libs/pbd/pbd/transmitter.h
+++ b/libs/pbd/pbd/transmitter.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libmisc_transmitter_h__
-#define __libmisc_transmitter_h__
+#pragma once
 
 #include <sstream>
 #include <iostream>
@@ -105,4 +104,3 @@ endmsg (std::ostream &ostr)
 
 extern "C" { LIBPBD_API void pbd_c_error (const char *); }
 
-#endif // __libmisc_transmitter_h__
diff --git a/libs/pbd/pbd/undo.h b/libs/pbd/pbd/undo.h
index 4736b31040..1eb75c89c5 100644
--- a/libs/pbd/pbd/undo.h
+++ b/libs/pbd/pbd/undo.h
@@ -20,8 +20,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __lib_pbd_undo_h__
-#define __lib_pbd_undo_h__
+#pragma once
 
 #include <list>
 #include <map>
@@ -146,4 +145,3 @@ private:
 
 } /* namespace */
 
-#endif /* __lib_pbd_undo_h__ */
diff --git a/libs/pbd/pbd/unknown_type.h b/libs/pbd/pbd/unknown_type.h
index 1caba54b9c..544d31276b 100644
--- a/libs/pbd/pbd/unknown_type.h
+++ b/libs/pbd/pbd/unknown_type.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __pbd_unknown_type_h__
-#define __pbd_unknown_type_h__
+#pragma once
 
 #include <exception>
 
@@ -28,4 +27,3 @@ class /*LIBPBD_API*/ unknown_type : public std::exception {
 	virtual const char *what() const throw() { return "unknown type"; }
 };
 
-#endif /* __pbd_unknown_type_h__ */
diff --git a/libs/pbd/pbd/unwind.h b/libs/pbd/pbd/unwind.h
index 4abe0f32fe..5768484d4c 100644
--- a/libs/pbd/pbd/unwind.h
+++ b/libs/pbd/pbd/unwind.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libpbd_unwinder_h__
-#define __libpbd_unwinder_h__
+#pragma once
 
 #include "pbd/libpbd_visibility.h"
 
@@ -46,4 +45,3 @@ class /*LIBPBD_API*/ ExceptionSafeIncDec {
 
 }
 
-#endif /* __libpbd_unwinder_h__ */
diff --git a/libs/pbd/pbd/uuid.h b/libs/pbd/pbd/uuid.h
index b80da66ba2..890c9db6b7 100644
--- a/libs/pbd/pbd/uuid.h
+++ b/libs/pbd/pbd/uuid.h
@@ -18,8 +18,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __pbd_uuid_h__
-#define __pbd_uuid_h__
+#pragma once
 
 #include <string>
 #include <boost/uuid/uuid.hpp>
@@ -49,4 +48,3 @@ class LIBPBD_API UUID : public boost::uuids::uuid {
 
 } // namespace PBD
 
-#endif // __pbd_uuid_h__
diff --git a/libs/pbd/pbd/uuid_boost.h b/libs/pbd/pbd/uuid_boost.h
index fd68ff8222..3baae16501 100644
--- a/libs/pbd/pbd/uuid_boost.h
+++ b/libs/pbd/pbd/uuid_boost.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __pbd_uuid_h__
-#define __pbd_uuid_h__
+#pragma once
 
 #include <string>
 #include <boost/uuid/uuid.hpp>
@@ -56,4 +55,3 @@ class LIBPBD_API UUID : public boost::uuids::uuid {
 
 } // namespace PBD
 
-#endif // __pbd_uuid_h__
diff --git a/libs/pbd/pbd/whitespace.h b/libs/pbd/pbd/whitespace.h
index cc4b2d944f..9968f1b43f 100644
--- a/libs/pbd/pbd/whitespace.h
+++ b/libs/pbd/pbd/whitespace.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __pbd_whitespace_h__
-#define __pbd_whitespace_h__
+#pragma once
 
 #include <string>
 
@@ -32,4 +31,3 @@ namespace PBD {
 	LIBPBD_API extern void remove_extra_whitespace (std::string const & in, std::string & out);
 } // namespace PBD
 
-#endif // __pbd_whitespace_h__
diff --git a/libs/pbd/pbd/windows_special_dirs.h b/libs/pbd/pbd/windows_special_dirs.h
index 146ad747a8..179fef1014 100644
--- a/libs/pbd/pbd/windows_special_dirs.h
+++ b/libs/pbd/pbd/windows_special_dirs.h
@@ -19,8 +19,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libpbd_windows_special_dirs_h__
-#define __libpbd_windows_special_dirs_h__
+#pragma once
 
 #include <windows.h>
 #include <string>
@@ -47,4 +46,3 @@ LIBPBD_API bool windows_query_registry (const char* regkey, const char* regval,
 
 }
 
-#endif /* __libpbd_windows_special_dirs_h__ */
diff --git a/libs/temporal/temporal/bbt_argument.h b/libs/temporal/temporal/bbt_argument.h
index 04d3da2c9b..28ee3cc7cb 100644
--- a/libs/temporal/temporal/bbt_argument.h
+++ b/libs/temporal/temporal/bbt_argument.h
@@ -16,8 +16,7 @@
   Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */
 
-#ifndef __libtemporal_bbt_argument_h__
-#define __libtemporal_bbt_argument_h__
+#pragma once
 
 #include "temporal/bbt_time.h"
 #include "temporal/timeline.h"
@@ -51,4 +50,3 @@ LIBTEMPORAL_API std::ostream& operator<< (std::ostream& o, Temporal::BBT_Argumen
 
 }
 
-#endif /* __libtemporal_bbt_argument_h__ */
diff --git a/libs/temporal/temporal/bbt_time.h b/libs/temporal/temporal/bbt_time.h
index b7206c4348..4ff1f18f3c 100644
--- a/libs/temporal/temporal/bbt_time.h
+++ b/libs/temporal/temporal/bbt_time.h
@@ -16,8 +16,7 @@
   Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */
 
-#ifndef __libtemporal_bbt_time_h__
-#define __libtemporal_bbt_time_h__
+#pragma once
 
 #include <ostream>
 #include <istream>
@@ -429,4 +428,3 @@ inline Temporal::BBT_Offset string_to (std::string const & str)
 
 } /* end namespace PBD */
 
-#endif /* __libtemporal_bbt_time_h__ */
diff --git a/libs/temporal/temporal/debug.h b/libs/temporal/temporal/debug.h
index 7ea1583fb6..d8153dd000 100644
--- a/libs/temporal/temporal/debug.h
+++ b/libs/temporal/temporal/debug.h
@@ -17,8 +17,7 @@
 
 */
 
-#ifndef __temporal_debug_h__
-#define __temporal_debug_h__
+#pragma once
 
 #include "temporal/visibility.h"
 #include "pbd/debug.h"
@@ -34,5 +33,4 @@ namespace PBD {
 	}
 }
 
-#endif /* __ardour_debug_h__ */
 
diff --git a/libs/temporal/temporal/domain_provider.h b/libs/temporal/temporal/domain_provider.h
index b396165288..3ac46c76c5 100644
--- a/libs/temporal/temporal/domain_provider.h
+++ b/libs/temporal/temporal/domain_provider.h
@@ -16,8 +16,7 @@
     Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */
 
-#ifndef __temporal_domain_provider_h__
-#define __temporal_domain_provider_h__
+#pragma once
 
 #include "pbd/signals.h"
 #include "pbd/stateful.h"
@@ -99,4 +98,3 @@ class TimeDomainProvider  {
 
 }
 
-#endif /* __temporal_domain_provider_h__ */
diff --git a/libs/temporal/temporal/domain_swap.h b/libs/temporal/temporal/domain_swap.h
index b9a0572156..e1428de457 100644
--- a/libs/temporal/temporal/domain_swap.h
+++ b/libs/temporal/temporal/domain_swap.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __temporal_domain_swap_h__
-#define __temporal_domain_swap_h__
+#pragma once
 
 #include <set>
 
@@ -70,4 +69,3 @@ struct LIBTEMPORAL_API DomainBounceInfo
 
 }
 
-#endif /* __tmeporal_domain_swap_h__ */
diff --git a/libs/temporal/temporal/superclock.h b/libs/temporal/temporal/superclock.h
index 9ebf4a9163..a3f4783f30 100644
--- a/libs/temporal/temporal/superclock.h
+++ b/libs/temporal/temporal/superclock.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __ardour_superclock_h__
-#define __ardour_superclock_h__
+#pragma once
 
 #include <stdint.h>
 
@@ -58,4 +57,3 @@ LIBTEMPORAL_API void set_superclock_ticks_per_second (superclock_t sc);
 
 #define TEMPORAL_SAMPLE_RATE (Temporal::most_recent_engine_sample_rate)
 
-#endif /* __ardour_superclock_h__ */
diff --git a/libs/temporal/temporal/tempo.h b/libs/temporal/temporal/tempo.h
index 549749fc82..7454d4f82d 100644
--- a/libs/temporal/temporal/tempo.h
+++ b/libs/temporal/temporal/tempo.h
@@ -16,8 +16,7 @@
     Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */
 
-#ifndef __temporal_tempo_h__
-#define __temporal_tempo_h__
+#pragma once
 
 #include <list>
 #include <string>
@@ -1296,4 +1295,3 @@ LIBTEMPORAL_API std::ostream& operator<<(std::ostream& str, Temporal::MusicTimeP
 LIBTEMPORAL_API std::ostream& operator<<(std::ostream& str, Temporal::TempoMetric const &);
 }
 
-#endif /* __temporal_tempo_h__ */
diff --git a/libs/temporal/temporal/time.h b/libs/temporal/temporal/time.h
index e527965d99..bef284eecc 100644
--- a/libs/temporal/temporal/time.h
+++ b/libs/temporal/temporal/time.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __timecode_time_h__
-#define __timecode_time_h__
+#pragma once
 
 #include <cmath>
 #include <inttypes.h>
@@ -166,4 +165,3 @@ sample_to_timecode (
 
 extern LIBTEMPORAL_API std::ostream& operator<< (std::ostream& ostr, const Timecode::Time& t);
 
-#endif // __timecode_time_h__
diff --git a/libs/temporal/temporal/timeline.h b/libs/temporal/temporal/timeline.h
index 5bac31e928..ccd2a0d175 100644
--- a/libs/temporal/temporal/timeline.h
+++ b/libs/temporal/temporal/timeline.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libtemporal_timeline_h__
-#define __libtemporal_timeline_h__
+#pragma once
 
 #include <ostream>
 #include <exception>
@@ -499,4 +498,3 @@ inline static bool operator>= (Temporal::Beats const & b, Temporal::timecnt_t co
 
 #undef TEMPORAL_DOMAIN_WARNING
 
-#endif /* __libtemporal_timeline_h__ */
diff --git a/libs/temporal/temporal/types.h b/libs/temporal/temporal/types.h
index df02b7fd78..0079f67bfb 100644
--- a/libs/temporal/temporal/types.h
+++ b/libs/temporal/temporal/types.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libpbd_position_types_h__
-#define __libpbd_position_types_h__
+#pragma once
 
 #include <cstdlib>
 #include <stdint.h>
@@ -130,4 +129,3 @@ extern void setup_enum_writer ();
 
 std::ostream& operator<< (std::ostream& o, Temporal::ratio_t const & r);
 
-#endif /* __libpbd_position_types_h__ */
diff --git a/libs/temporal/temporal/visibility.h b/libs/temporal/temporal/visibility.h
index b9ba81a074..e378e21b4b 100644
--- a/libs/temporal/temporal/visibility.h
+++ b/libs/temporal/temporal/visibility.h
@@ -16,8 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libtimecode_visibility_h__
-#define __libtimecode_visibility_h__
+#pragma once
 
 #if defined(COMPILER_MSVC)
   #define LIBTEMPORAL_DLL_IMPORT __declspec(dllimport)
@@ -42,4 +41,3 @@
 #endif
 #define LIBTEMPORAL_LOCAL LIBTEMPORAL_DLL_LOCAL
 
-#endif /* __libtimecode_visibility_h__ */
diff --git a/libs/waveview/waveview/visibility.h b/libs/waveview/waveview/visibility.h
index 829b6a0bce..594d5cae70 100644
--- a/libs/waveview/waveview/visibility.h
+++ b/libs/waveview/waveview/visibility.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libwaveview_visibility_h__
-#define __libwaveview_visibility_h__
+#pragma once
 
 #if defined(COMPILER_MSVC)
   #define LIBWAVEVIEW_DLL_IMPORT __declspec(dllimport)
@@ -42,4 +41,3 @@
   #define LIBWAVEVIEW_LOCAL LIBWAVEVIEW_DLL_LOCAL
 #endif
 
-#endif /* __libwaveview_visibility_h__ */
diff --git a/libs/widgets/widgets/visibility.h b/libs/widgets/widgets/visibility.h
index c3acbf11af..cfeefebe13 100644
--- a/libs/widgets/widgets/visibility.h
+++ b/libs/widgets/widgets/visibility.h
@@ -17,8 +17,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#ifndef __libwidgets_visibility_h__
-#define __libwidgets_visibility_h__
+#pragma once
 
 #if defined(COMPILER_MSVC)
   #define LIBWIDGETS_DLL_IMPORT __declspec(dllimport)
@@ -42,4 +41,3 @@
   #define LIBWIDGETS_LOCAL LIBWIDGETS_DLL_LOCAL
 #endif
 
-#endif /* __libwidgets_visibility_h__ */