diff --git a/libs/ardour/beats_frames_converter.cc b/libs/ardour/beats_frames_converter.cc
index 584732ff03..62a0ebde69 100644
--- a/libs/ardour/beats_frames_converter.cc
+++ b/libs/ardour/beats_frames_converter.cc
@@ -19,6 +19,8 @@
     $Id: midiregion.h 733 2006-08-01 17:19:38Z drobilla $
 */
 
+#include "pbd/stacktrace.h"
+
 #include "ardour/beats_frames_converter.h"
 #include "ardour/tempo.h"
 
@@ -31,6 +33,10 @@ namespace ARDOUR {
 framecnt_t
 BeatsFramesConverter::to (double beats) const
 {
+	if (beats < 0) {
+		std::cerr << "negative beats passed to BFC: " << beats << std::endl;
+		PBD::stacktrace (std::cerr, 30);
+	}
 	assert (beats >= 0);
 	framecnt_t r = _tempo_map.framepos_plus_beats (_origin_b, beats) - _origin_b;
 	return r;