diff --git a/libs/ardour/audioengine.cc b/libs/ardour/audioengine.cc
index 67f1f15c4d..6176ebd4df 100644
--- a/libs/ardour/audioengine.cc
+++ b/libs/ardour/audioengine.cc
@@ -205,7 +205,9 @@ AudioEngine::process_callback (pframes_t nframes)
 
 	if (!tm.locked()) {
 		/* return having done nothing */
-		Xrun();
+		if (_session) {
+			Xrun();
+		}
 		_processed_frames = next_processed_frames;
 		return 0;
 	}