--- a/dom/html/HTMLMediaElement.cpp
+++ b/dom/html/HTMLMediaElement.cpp
@@ -1690,16 +1690,17 @@ void HTMLMediaElement::AbortExistingLoad
 void HTMLMediaElement::NoSupportedMediaSourceError(const nsACString& aErrorDetails)
 {
   if (mDecoder) {
     ShutdownDecoder();
   }
   mErrorSink->SetError(MEDIA_ERR_SRC_NOT_SUPPORTED, aErrorDetails);
   ChangeDelayLoadStatus(false);
   UpdateAudioChannelPlayingState();
+  RejectPromises(TakePendingPlayPromises(), NS_ERROR_DOM_MEDIA_NOT_SUPPORTED_ERR);
 }
 
 typedef void (HTMLMediaElement::*SyncSectionFn)();
 
 // Runs a "synchronous section", a function that must run once the event loop
 // has reached a "stable state". See:
 // http://www.whatwg.org/specs/web-apps/current-work/multipage/webappapis.html#synchronous-section
 class nsSyncSection : public nsMediaEvent

--- a/dom/html/HTMLMediaElement.h
+++ b/dom/html/HTMLMediaElement.h
@@ -951,16 +951,17 @@ protected:
   /**
    * Execute the initial steps of the load algorithm that ensure existing
    * loads are aborted, the element is emptied, and a new load ID is
    * created.
    */
   void AbortExistingLoads();
 
   /**
+   * This is the dedicated media source failure steps.
    * Called when all potential resources are exhausted. Changes network
    * state to NETWORK_NO_SOURCE, and sends error event with code
    * MEDIA_ERR_SRC_NOT_SUPPORTED.
    */
   void NoSupportedMediaSourceError(const nsACString& aErrorDetails = nsCString());
 
   /**
    * Attempts to load resources from the <source> children. This is a