diff --git a/dom/media/DOMMediaStream.cpp b/dom/media/DOMMediaStream.cpp
index 5f0f097aee7d..ca001c8851f1 100644
--- a/dom/media/DOMMediaStream.cpp
+++ b/dom/media/DOMMediaStream.cpp
@@ -411,7 +411,7 @@ DOMMediaStream::DOMMediaStream(nsPIDOMWindowInner* aWindow,
     mPlaybackTrackListener(MakeAndAddRef<PlaybackTrackListener>(this)),
     mTracksCreated(false), mNotifiedOfMediaStreamGraphShutdown(false),
     mActive(false), mSetInactiveOnFinish(false),
-    mAbstractMainThread(aWindow->GetDocGroup()->AbstractMainThreadFor(TaskCategory::Other))
+    mAbstractMainThread(aWindow ? aWindow->GetDocGroup()->AbstractMainThreadFor(TaskCategory::Other) : nullptr)
 {
   nsresult rv;
   nsCOMPtr<nsIUUIDGenerator> uuidgen =
@@ -855,6 +855,7 @@ DOMMediaStream::SetInactiveOnFinish()
 void
 DOMMediaStream::InitSourceStream(MediaStreamGraph* aGraph)
 {
+  MOZ_ASSERT(mAbstractMainThread);
   InitInputStreamCommon(aGraph->CreateSourceStream(mAbstractMainThread), aGraph);
   InitOwnedStreamCommon(aGraph);
   InitPlaybackStreamCommon(aGraph);
@@ -863,6 +864,7 @@ DOMMediaStream::InitSourceStream(MediaStreamGraph* aGraph)
 void
 DOMMediaStream::InitTrackUnionStream(MediaStreamGraph* aGraph)
 {
+  MOZ_ASSERT(mAbstractMainThread);
   InitInputStreamCommon(aGraph->CreateTrackUnionStream(mAbstractMainThread), aGraph);
   InitOwnedStreamCommon(aGraph);
   InitPlaybackStreamCommon(aGraph);
@@ -871,6 +873,7 @@ DOMMediaStream::InitTrackUnionStream(MediaStreamGraph* aGraph)
 void
 DOMMediaStream::InitAudioCaptureStream(nsIPrincipal* aPrincipal, MediaStreamGraph* aGraph)
 {
+  MOZ_ASSERT(mAbstractMainThread);
   const TrackID AUDIO_TRACK = 1;
 
   RefPtr<BasicTrackSource> audioCaptureSource =
@@ -901,6 +904,7 @@ DOMMediaStream::InitInputStreamCommon(MediaStream* aStream,
 void
 DOMMediaStream::InitOwnedStreamCommon(MediaStreamGraph* aGraph)
 {
+  MOZ_ASSERT(mAbstractMainThread);
   MOZ_ASSERT(!mPlaybackStream, "Owned stream must be initialized before playback stream");
 
   mOwnedStream = aGraph->CreateTrackUnionStream(mAbstractMainThread);
@@ -918,6 +922,7 @@ DOMMediaStream::InitOwnedStreamCommon(MediaStreamGraph* aGraph)
 void
 DOMMediaStream::InitPlaybackStreamCommon(MediaStreamGraph* aGraph)
 {
+  MOZ_ASSERT(mAbstractMainThread);
   mPlaybackStream = aGraph->CreateTrackUnionStream(mAbstractMainThread);
   mPlaybackStream->SetAutofinish(true);
   mPlaybackStream->RegisterUser();