diff --git a/libs/ardour/audio_unit.cc b/libs/ardour/audio_unit.cc
index 230482551b..70d2853f8c 100644
--- a/libs/ardour/audio_unit.cc
+++ b/libs/ardour/audio_unit.cc
@@ -1760,9 +1760,8 @@ AUPlugin::get_beat_and_tempo_callback (Float64* outCurrentBeat,
 		return kAudioUnitErr_CannotDoInCurrentContext;
 	}
 
-	Timecode::BBT_Time bbt;
 	TempoMetric metric = tmap.metric_at (_session.transport_frame() + input_offset);
-	tmap.bbt_time (_session.transport_frame() + input_offset, bbt);
+	Timecode::BBT_Time bbt = _session.tempo_map().bbt_at_frame (_session.transport_frame() + input_offset);
 
 	if (outCurrentBeat) {
 		const double ppq_scaling = metric.meter().note_divisor() / 4.0;
@@ -1800,9 +1799,8 @@ AUPlugin::get_musical_time_location_callback (UInt32*   outDeltaSampleOffsetToNe
 		return kAudioUnitErr_CannotDoInCurrentContext;
 	}
 
-	Timecode::BBT_Time bbt;
 	TempoMetric metric = tmap.metric_at (_session.transport_frame() + input_offset);
-	tmap.bbt_time (_session.transport_frame() + input_offset, bbt);
+	Timecode::BBT_Time bbt = _session.tempo_map().bbt_at_frame (_session.transport_frame() + input_offset);
 
 	if (outDeltaSampleOffsetToNextBeat) {
 		if (bbt.ticks == 0) {
@@ -1896,7 +1894,7 @@ AUPlugin::get_transport_state_callback (Boolean*  outIsPlaying,
 
 				if (outCycleStartBeat) {
 					TempoMetric metric = tmap.metric_at (loc->start() + input_offset);
-					_session.tempo_map().bbt_time (loc->start(), bbt);
+					bbt = _session.tempo_map().bbt_at_frame (loc->start() + input_offset);
 
 					float beat;
 					beat = metric.meter().divisions_per_bar() * bbt.bars;
@@ -1908,7 +1906,7 @@ AUPlugin::get_transport_state_callback (Boolean*  outIsPlaying,
 
 				if (outCycleEndBeat) {
 					TempoMetric metric = tmap.metric_at (loc->end() + input_offset);
-					_session.tempo_map().bbt_time (loc->end(), bbt);
+					bbt = _session.tempo_map().bbt_at_frame (loc->end() + input_offset);
 
 					float beat;
 					beat = metric.meter().divisions_per_bar() * bbt.bars;