diff --git a/libs/ardour/ardour/audio_buffer.h b/libs/ardour/ardour/audio_buffer.h
index 051b75ab4b..9a9653b2c9 100644
--- a/libs/ardour/ardour/audio_buffer.h
+++ b/libs/ardour/ardour/audio_buffer.h
@@ -220,7 +220,13 @@ public:
 	 */
 	bool check_silence (pframes_t nframes, pframes_t& n) const;
 
-	void prepare () { _written = false; _silent = false; }
+	void prepare () {
+		if (!_owns_data) {
+			_data = 0;
+		}
+		_written = false;
+		_silent = false;
+	}
 	bool written() const { return _written; }
 	void set_written(bool w) { _written = w; }
 
diff --git a/libs/ardour/audio_port.cc b/libs/ardour/audio_port.cc
index e2bb20dbe9..33e41c10ad 100644
--- a/libs/ardour/audio_port.cc
+++ b/libs/ardour/audio_port.cc
@@ -59,8 +59,11 @@ void
 AudioPort::cycle_end (pframes_t nframes)
 {
         if (sends_output() && !_buffer->written()) {
-		if (_buffer->capacity() >= nframes) {
-			_buffer->silence (nframes);
+	        if (!_buffer->data (0)) {
+		        get_audio_buffer (nframes);
+	        }
+	        if (_buffer->capacity() >= nframes) {
+		        _buffer->silence (nframes);
 		}
 	}
 }