diff --git a/libs/ardour/triggerbox.cc b/libs/ardour/triggerbox.cc
index a16466727f..a1d472ca79 100644
--- a/libs/ardour/triggerbox.cc
+++ b/libs/ardour/triggerbox.cc
@@ -2470,7 +2470,11 @@ MIDITrigger::setup_event_indices ()
 {
 	RTMidiBufferBeats* rt = rt_midibuffer.load ();
 
-	assert (rt->size() > 0);
+	if (rt->size() == 0) {
+		first_event_index = 0;
+		last_event_index = 0;
+		return;
+	}
 
 	if (rt->size() == 1) {
 		first_event_index = 0;