--- a/dom/media/mediasource/TrackBuffersManager.cpp
+++ b/dom/media/mediasource/TrackBuffersManager.cpp
@@ -886,16 +886,17 @@ TrackBuffersManager::OnDemuxerInitDone(n
   MOZ_ASSERT(OnTaskQueue());
   mDemuxerInitRequest.Complete();
 
   if (!mInputDemuxer) {
     // mInputDemuxer shouldn't have been destroyed while a demuxer init/reset
     // request was being processed. See bug 1239983.
     NS_ASSERTION(false, "mInputDemuxer has been destroyed");
     RejectAppend(NS_ERROR_ABORT, __func__);
+    return;
   }
 
   MediaInfo info;
 
   uint32_t numVideos = mInputDemuxer->GetNumberTracks(TrackInfo::kVideoTrack);
   if (numVideos) {
     // We currently only handle the first video track.
     mVideoTracks.mDemuxer = mInputDemuxer->GetTrackDemuxer(TrackInfo::kVideoTrack, 0);