--- a/dom/html/HTMLMediaElement.cpp
+++ b/dom/html/HTMLMediaElement.cpp
@@ -2205,21 +2205,25 @@ public:
                                            MediaStreamTrackSource)
 
   explicit StreamCaptureTrackSource(MediaStreamTrackSource* aCapturedTrackSource)
     : MediaStreamTrackSource(aCapturedTrackSource->GetPrincipal(),
                              true,
                              nsString())
     , mCapturedTrackSource(aCapturedTrackSource)
   {
+    mCapturedTrackSource->RegisterSink(this);
   }
 
   void Destroy() override
   {
     MOZ_ASSERT(mCapturedTrackSource);
+    if (mCapturedTrackSource) {
+      mCapturedTrackSource->UnregisterSink(this);
+    }
   }
 
   MediaSourceEnum GetMediaSource() const override
   {
     return MediaSourceEnum::Other;
   }
 
   CORSMode GetCORSMode() const override