--- a/dom/media/MediaStreamGraph.cpp
+++ b/dom/media/MediaStreamGraph.cpp
@@ -4010,32 +4010,20 @@ MediaStreamGraphImpl::ApplyAudioContextO
         driver = new SystemClockDriver(this);
         MonitorAutoLock lock(mMonitor);
         CurrentDriver()->SwitchAtNextIteration(driver);
       }
       // We are closing or suspending an AudioContext, but we just got resumed.
       // Queue the operation on the next driver so that the ordering is
       // preserved.
     } else if (!audioTrackPresent && switching) {
-      MOZ_ASSERT(nextDriver->AsAudioCallbackDriver() ||
-                 nextDriver->AsSystemClockDriver()->IsFallback());
-      if (nextDriver->AsAudioCallbackDriver()) {
-        nextDriver->AsAudioCallbackDriver()->
-          EnqueueStreamAndPromiseForOperation(aDestinationStream, aPromise,
-                                              aOperation);
-      }
-      // If this is not an AudioCallbackDriver, this means we failed opening an
-      // AudioCallbackDriver in the past, and we're constantly trying to re-open
-      // an new audio stream, but are running this graph that has an audio track
-      // off a SystemClockDriver for now to keep things moving.  This is the
-      // case where we're trying to switch an an system driver (because suspend
-      // or close have been called on an AudioContext, or we've closed the
-      // page), but we're already running one. We can just resolve the promise
-      // now: we're already running off a system thread.
-      AudioContextOperationCompleted(aDestinationStream, aPromise, aOperation);
+      MOZ_ASSERT(nextDriver->AsAudioCallbackDriver());
+      nextDriver->AsAudioCallbackDriver()->
+        EnqueueStreamAndPromiseForOperation(aDestinationStream, aPromise,
+                                            aOperation);
     } else {
       // We are closing or suspending an AudioContext, but something else is
       // using the audio stream, we can resolve the promise now.
       AudioContextOperationCompleted(aDestinationStream, aPromise, aOperation);
     }
   }
 }