diff --git a/src/emu/sound.h b/src/emu/sound.h
index 60fca2c683f..b13d5b31d9a 100644
--- a/src/emu/sound.h
+++ b/src/emu/sound.h
@@ -22,6 +22,7 @@
 //  MACROS
 //**************************************************************************
 
+// legacy
 #define STREAM_UPDATE(name) void name(device_t *device, sound_stream *stream, void *param, stream_sample_t **inputs, stream_sample_t **outputs, int samples)