diff --git a/content/media/MediaStreamGraph.cpp b/content/media/MediaStreamGraph.cpp
index 893d87fc0b8..9a7a03a3eac 100644
--- a/content/media/MediaStreamGraph.cpp
+++ b/content/media/MediaStreamGraph.cpp
@@ -1748,6 +1748,7 @@ SourceMediaStream::AdvanceKnownTracksTime(StreamTime aKnownTime)
 void
 SourceMediaStream::FinishWithLockHeld()
 {
+  mMutex.AssertCurrentThreadOwns();
   mUpdateFinished = true;
   if (!mDestroyed) {
     GraphImpl()->EnsureNextIteration();
@@ -1757,12 +1758,10 @@ SourceMediaStream::FinishWithLockHeld()
 void
 SourceMediaStream::EndAllTrackAndFinish()
 {
-  {
-    MutexAutoLock lock(mMutex);
-    for (uint32_t i = 0; i < mUpdateTracks.Length(); ++i) {
-      SourceMediaStream::TrackData* data = &mUpdateTracks[i];
-      data->mCommands |= TRACK_END;
-    }
+  MutexAutoLock lock(mMutex);
+  for (uint32_t i = 0; i < mUpdateTracks.Length(); ++i) {
+    SourceMediaStream::TrackData* data = &mUpdateTracks[i];
+    data->mCommands |= TRACK_END;
   }
   FinishWithLockHeld();
   // we will call NotifyFinished() to let GetUserMedia know