diff --git a/content/media/DOMMediaStream.cpp b/content/media/DOMMediaStream.cpp
index 9fdaf090931..e99ac451790 100644
--- a/content/media/DOMMediaStream.cpp
+++ b/content/media/DOMMediaStream.cpp
@@ -324,6 +324,9 @@ DOMMediaStream::OnTracksAvailable(OnTracksAvailableCallback* aRunnable)
 void
 DOMMediaStream::CheckTracksAvailable()
 {
+  if (mTrackTypesAvailable == 0) {
+    return;
+  }
   nsTArray<nsAutoPtr<OnTracksAvailableCallback> > callbacks;
   callbacks.SwapElements(mRunOnTracksAvailable);
 
diff --git a/content/media/DOMMediaStream.h b/content/media/DOMMediaStream.h
index 641be783ac6..f7bd781594b 100644
--- a/content/media/DOMMediaStream.h
+++ b/content/media/DOMMediaStream.h
@@ -164,6 +164,7 @@ public:
   // We only care about track additions, we'll fire the notification even if
   // some of the tracks have been removed.
   // Takes ownership of aCallback.
+  // If GetExpectedTracks() returns 0, the callback will be fired as soon as there are any tracks.
   void OnTracksAvailable(OnTracksAvailableCallback* aCallback);
 
   /**
@@ -182,6 +183,7 @@ protected:
   void InitSourceStream(nsIDOMWindow* aWindow, TrackTypeHints aHintContents);
   void InitTrackUnionStream(nsIDOMWindow* aWindow, TrackTypeHints aHintContents);
   void InitStreamCommon(MediaStream* aStream);
+
   void CheckTracksAvailable();
 
   class StreamListener;