diff --git a/libs/ardour/delayline.cc b/libs/ardour/delayline.cc
index 8e24fd55ec..550051f2d0 100644
--- a/libs/ardour/delayline.cc
+++ b/libs/ardour/delayline.cc
@@ -115,6 +115,7 @@ DelayLine::run (BufferSet& bufs, framepos_t /* start_frame */, framepos_t /* end
 		_buf = _pending_buf;
 		_bsiz = _pending_bsiz;
 		_pending_bsiz = 0;
+		_pending_buf.reset();
 	}
 
 	/* there may be no buffer when delay == 0.