diff --git a/dom/media/MediaDecoderStateMachine.cpp b/dom/media/MediaDecoderStateMachine.cpp
index 5e8e3941e6a..85f3ce055e2 100644
--- a/dom/media/MediaDecoderStateMachine.cpp
+++ b/dom/media/MediaDecoderStateMachine.cpp
@@ -836,6 +836,10 @@ MediaDecoderStateMachine::OnNotDecoded(MediaData::Type aType,
   } else {
     mVideoDataRequest.Complete();
   }
+  if (IsShutdown()) {
+    // Already shutdown;
+    return;
+  }
 
   // If this is a decode error, delegate to the generic error path.
   if (aReason == MediaDecoderReader::DECODE_ERROR) {
@@ -1927,6 +1931,10 @@ MediaDecoderStateMachine::DispatchAudioDecodeTaskIfNeeded()
   MOZ_ASSERT(OnStateMachineThread());
   ReentrantMonitorAutoEnter mon(mDecoder->GetReentrantMonitor());
 
+  if (IsShutdown()) {
+    return NS_ERROR_FAILURE;
+  }
+
   if (NeedToDecodeAudio()) {
     return EnsureAudioDecodeTaskQueued();
   }
@@ -1973,6 +1981,10 @@ MediaDecoderStateMachine::DispatchVideoDecodeTaskIfNeeded()
   MOZ_ASSERT(OnStateMachineThread());
   ReentrantMonitorAutoEnter mon(mDecoder->GetReentrantMonitor());
 
+  if (IsShutdown()) {
+    return NS_ERROR_FAILURE;
+  }
+
   if (NeedToDecodeVideo()) {
     return EnsureVideoDecodeTaskQueued();
   }
diff --git a/dom/media/mediasource/MediaSourceReader.cpp b/dom/media/mediasource/MediaSourceReader.cpp
index 964c32af879..b7c261d7b7f 100644
--- a/dom/media/mediasource/MediaSourceReader.cpp
+++ b/dom/media/mediasource/MediaSourceReader.cpp
@@ -418,6 +418,14 @@ nsRefPtr<ShutdownPromise>
 MediaSourceReader::Shutdown()
 {
   mSeekPromise.RejectIfExists(NS_ERROR_FAILURE, __func__);
+  // Any previous requests we've been waiting on are now unwanted.
+  mAudioRequest.DisconnectIfExists();
+  mVideoRequest.DisconnectIfExists();
+
+  // Additionally, reject any outstanding promises _we_ made that we might have
+  // been waiting on the above to fulfill.
+  mAudioPromise.RejectIfExists(CANCELED, __func__);
+  mVideoPromise.RejectIfExists(CANCELED, __func__);
 
   MOZ_ASSERT(mMediaSourceShutdownPromise.IsEmpty());
   nsRefPtr<ShutdownPromise> p = mMediaSourceShutdownPromise.Ensure(__func__);