--- a/dom/media/MediaStreamTrack.cpp
+++ b/dom/media/MediaStreamTrack.cpp
@@ -409,16 +409,23 @@ MediaStreamTrack::NotifyEnded()
   MOZ_ASSERT(NS_IsMainThread());
 
   if (Ended()) {
     return;
   }
 
   LOG(LogLevel::Info, ("MediaStreamTrack %p ended", this));
 
+  if (!mSource) {
+    MOZ_ASSERT(false);
+    return;
+  }
+
+  mSource->UnregisterSink(this);
+
   mReadyState = MediaStreamTrackState::Ended;
 
   DispatchTrustedEvent(NS_LITERAL_STRING("ended"));
 }
 
 DOMMediaStream*
 MediaStreamTrack::GetInputDOMStream()
 {