diff --git a/libs/ardour/ardour/audio_unit.h b/libs/ardour/ardour/audio_unit.h
index 24f427b124..c5c5ed4a95 100644
--- a/libs/ardour/ardour/audio_unit.h
+++ b/libs/ardour/ardour/audio_unit.h
@@ -171,7 +171,7 @@ class LIBARDOUR_API AUPlugin : public ARDOUR::Plugin
 	int32_t output_channels;
 	std::vector<std::pair<int,int> > io_configs;
 	framecnt_t _last_nframes;
-	mutable framecnt_t _current_latency;
+	mutable volatile guint _current_latency;
 	bool _requires_fixed_size_buffers;
 	AudioBufferList* buffers;
 	bool _has_midi_input;
diff --git a/libs/ardour/audio_unit.cc b/libs/ardour/audio_unit.cc
index 3e6bdfb691..85a387e933 100644
--- a/libs/ardour/audio_unit.cc
+++ b/libs/ardour/audio_unit.cc
@@ -431,7 +431,7 @@ AUPlugin::AUPlugin (AudioEngine& engine, Session& session, boost::shared_ptr<CAC
 	, unit (new CAAudioUnit)
 	, initialized (false)
 	, _last_nframes (0)
-	, _current_latency (-1)
+	, _current_latency (UINT_MAX)
 	, _requires_fixed_size_buffers (false)
 	, buffers (0)
 	, variable_inputs (false)
@@ -472,7 +472,7 @@ AUPlugin::AUPlugin (const AUPlugin& other)
 	, unit (new CAAudioUnit)
 	, initialized (false)
 	, _last_nframes (0)
-	, _current_latency (-1)
+	, _current_latency (UINT_MAX)
 	, _requires_fixed_size_buffers (false)
 	, buffers (0)
 	, variable_inputs (false)
@@ -955,10 +955,12 @@ AUPlugin::default_value (uint32_t port)
 framecnt_t
 AUPlugin::signal_latency () const
 {
-	if (_current_latency < 0) {
-		_current_latency = unit->Latency() * _session.frame_rate();
+	guint lat = g_atomic_int_get (&_current_latency);;
+	if (lat == UINT_MAX) {
+		lat = unit->Latency() * _session.frame_rate();
+		g_atomic_int_set (&_current_latency, lat);
 	}
-	return _current_latency;
+	return lat;
 }
 
 void
@@ -3474,9 +3476,9 @@ AUPlugin::parameter_change_listener (void* /*arg*/, void* src, const AudioUnitEv
 {
 	if (event->mEventType == kAudioUnitEvent_PropertyChange) {
 		if (event->mArgument.mProperty.mPropertyID == kAudioUnitProperty_Latency) {
-			DEBUG_TRACE (DEBUG::AudioUnits, string_compose("AU Latency Change Event %1 <> %1\n", new_value, unit->Latency()));
-			// TODO atomically set //_current_latency = -1;
-			_current_latency = unit->Latency() * _session.frame_rate(); // TODO: check: new_value
+			DEBUG_TRACE (DEBUG::AudioUnits, string_compose("AU Latency Change Event %1 <> %2\n", new_value, unit->Latency()));
+			guint lat = unit->Latency() * _session.frame_rate();
+			g_atomic_int_set (&_current_latency, lat);
 		}
 		return;
 	}