diff --git a/libs/ardour/automation_watch.cc b/libs/ardour/automation_watch.cc
index 3778367e9e..20b6b093a9 100644
--- a/libs/ardour/automation_watch.cc
+++ b/libs/ardour/automation_watch.cc
@@ -201,7 +201,7 @@ AutomationWatch::timer ()
 void
 AutomationWatch::thread ()
 {
-	pbd_set_thread_priority (pthread_self(), PBD_SCHED_FIFO, AudioEngine::instance()->client_real_time_priority() - 2); // XXX
+	pbd_set_thread_priority (pthread_self(), PBD_SCHED_FIFO, PBD_RT_PRI_CTRL);
 	while (_run_thread) {
 		Glib::usleep ((gulong) floor (Config->get_automation_interval_msecs() * 1000)); // TODO use pthread_cond_timedwait on _run_thread
 		timer ();
diff --git a/libs/ardour/convolver.cc b/libs/ardour/convolver.cc
index ee4fff453d..9dd1dfecf6 100644
--- a/libs/ardour/convolver.cc
+++ b/libs/ardour/convolver.cc
@@ -169,7 +169,7 @@ Convolution::restart ()
 	}
 
 	if (rv == 0) {
-		rv = _convproc.start_process (pbd_absolute_rt_priority (PBD_SCHED_FIFO, AudioEngine::instance ()->client_real_time_priority () - 1), PBD_SCHED_FIFO);
+		rv = _convproc.start_process (pbd_absolute_rt_priority (PBD_SCHED_FIFO, PBD_RT_PRI_PROC), PBD_SCHED_FIFO);
 	}
 
 	assert (rv == 0); // bail out in debug builds
diff --git a/libs/ardour/globals.cc b/libs/ardour/globals.cc
index 22166d7eea..a017ff7d3b 100644
--- a/libs/ardour/globals.cc
+++ b/libs/ardour/globals.cc
@@ -815,7 +815,7 @@ ARDOUR::init_post_engine (uint32_t start_cnt)
 		}
 	}
 
-	BaseUI::set_thread_priority (pbd_absolute_rt_priority (PBD_SCHED_FIFO, AudioEngine::instance()->client_real_time_priority () - 2));
+	BaseUI::set_thread_priority (pbd_absolute_rt_priority (PBD_SCHED_FIFO, PBD_RT_PRI_CTRL));
 
 	TransportMasterManager::instance ().restart ();
 }
diff --git a/libs/ardour/lv2_plugin.cc b/libs/ardour/lv2_plugin.cc
index 1121334159..de01e94245 100644
--- a/libs/ardour/lv2_plugin.cc
+++ b/libs/ardour/lv2_plugin.cc
@@ -607,7 +607,7 @@ LV2Plugin::init(const void* c_plugin, samplecnt_t rate)
 	static const int32_t _min_block_length = 1;   // may happen during split-cycles
 	static const int32_t _max_block_length = 8192; // max possible (with all engines and during export)
 	static const int32_t rt_policy = PBD_SCHED_FIFO;
-	static const int32_t rt_priority = pbd_absolute_rt_priority (PBD_SCHED_FIFO, AudioEngine::instance()->client_real_time_priority () - 1);
+	static const int32_t rt_priority = pbd_absolute_rt_priority (PBD_SCHED_FIFO, PBD_RT_PRI_PROC);
 	static const int32_t hw_concurrency = how_many_dsp_threads ();
 	/* Consider updating max-block-size whenever the buffersize changes.
 	 * It requires re-instantiating the plugin (which is a non-realtime operation),
diff --git a/libs/pbd/base_ui.cc b/libs/pbd/base_ui.cc
index d6b37f3657..4b4a65edb7 100644
--- a/libs/pbd/base_ui.cc
+++ b/libs/pbd/base_ui.cc
@@ -50,7 +50,7 @@ using namespace PBD;
 using namespace Glib;
 
 uint64_t BaseUI::rt_bit = 1;
-int BaseUI::_thread_priority = PBD_RT_PRI_PROC - 1;
+int BaseUI::_thread_priority = PBD_RT_PRI_CTRL;
 
 BaseUI::RequestType BaseUI::CallSlot = BaseUI::new_request_type();
 BaseUI::RequestType BaseUI::Quit = BaseUI::new_request_type();
diff --git a/libs/pbd/pbd/pthread_utils.h b/libs/pbd/pbd/pthread_utils.h
index 862340c548..a528363230 100644
--- a/libs/pbd/pbd/pthread_utils.h
+++ b/libs/pbd/pbd/pthread_utils.h
@@ -57,6 +57,7 @@
 # define PBD_RT_PRI_MAIN pbd_pthread_priority (THREAD_MAIN)
 # define PBD_RT_PRI_MIDI pbd_pthread_priority (THREAD_MIDI)
 # define PBD_RT_PRI_PROC pbd_pthread_priority (THREAD_PROC)
+# define PBD_RT_PRI_CTRL pbd_pthread_priority (THREAD_CTRL)
 
 LIBPBD_API int  pthread_create_and_store (std::string name, pthread_t  *thread, void * (*start_routine)(void *), void * arg, uint32_t stacklimit = 0x80000 /*512kB*/);
 LIBPBD_API void pthread_cancel_one (pthread_t thread);
@@ -65,10 +66,13 @@ LIBPBD_API void pthread_kill_all (int signum);
 LIBPBD_API const char* pthread_name ();
 LIBPBD_API void pthread_set_name (const char* name);
 
+LIBPBD_API void pbd_set_engine_rt_priority (int);
+
 enum PBDThreadClass {
 	THREAD_MAIN, // main audio I/O thread
 	THREAD_MIDI, // MIDI I/O threads
 	THREAD_PROC, // realtime worker
+	THREAD_CTRL, // Automation watch, BaseUI
 	THREAD_IO    // non-realtime I/O
 };