diff --git a/services/audioflinger/PlaybackTracks.h b/services/audioflinger/PlaybackTracks.h
index 6462a12..078ae12 100644
--- a/services/audioflinger/PlaybackTracks.h
+++ b/services/audioflinger/PlaybackTracks.h
@@ -469,7 +469,8 @@
      */
     SourceMetadatas mTrackMetadatas;
     /** Protects mTrackMetadatas against concurrent access. */
-    mutable audio_utils::mutex mTrackMetadatasMutex;
+    audio_utils::mutex& trackMetadataMutex() const { return mTrackMetadataMutex; }
+    mutable audio_utils::mutex mTrackMetadataMutex;
 };  // end of OutputTrack
 
 // playback track, used by PatchPanel