diff --git a/libs/ardour/session.cc b/libs/ardour/session.cc
index f55e95486e..eb8e233993 100644
--- a/libs/ardour/session.cc
+++ b/libs/ardour/session.cc
@@ -625,7 +625,7 @@ Session::destroy ()
 
 	ControlProtocolManager::instance().drop_protocols ();
 
-	/* stop autoconnecting */
+	/* stop auto dis/connecting */
 	auto_connect_thread_terminate ();
 
 	MIDI::Name::MidiPatchManager::instance().remove_search_path(session_directory().midi_patch_path());
@@ -807,6 +807,14 @@ Session::destroy ()
 		}
 	}
 
+	{
+		/* unregister all dropped ports, process pending port deletion. */
+		// this may call ARDOUR::Port::drop ... jack_port_unregister ()
+		// jack1 cannot cope with removing ports while processing
+		Glib::Threads::Mutex::Lock lm (AudioEngine::instance()->process_lock ());
+		AudioEngine::instance()->clear_pending_port_deletions ();
+	}
+
 	DEBUG_TRACE (DEBUG::Destruction, "Session::destroy() done\n");
 
 	BOOST_SHOW_POINTERS ();