diff --git a/chromecast/media/cma/pipeline/media_pipeline_impl.cc b/chromecast/media/cma/pipeline/media_pipeline_impl.cc
index fa6d002234ff5..87e383f838f02 100644
--- a/chromecast/media/cma/pipeline/media_pipeline_impl.cc
+++ b/chromecast/media/cma/pipeline/media_pipeline_impl.cc
@@ -369,12 +369,18 @@ void MediaPipelineImpl::OnFlushDone(bool is_audio_stream) {
 
   if (pending_flush_task_->audio_flushed &&
       pending_flush_task_->video_flushed) {
-    // Stop the backend, so that the backend won't push their pending buffer,
-    // which may be invalidated later, to hardware. (b/25342604)
-    media_pipeline_backend_->Stop();
-    backend_state_ = BACKEND_STATE_INITIALIZED;
-    metrics::CastMetricsHelper::GetInstance()->RecordApplicationEvent(
-        "Cast.Platform.Ended");
+    // Only Stop() and transition to INITIALIZED if the backend was actually
+    // started. A compromised renderer can call Renderer.Flush() before
+    // StartPlayingFrom(); without this guard we would call Stop() on a
+    // never-Initialize()d vendor backend and then permanently bypass the
+    // lazy Initialize() in StartPlayingFrom(). (b/25342604 still applies for
+    // the started case.)
+    if (backend_state_ != BACKEND_STATE_UNINITIALIZED) {
+      media_pipeline_backend_->Stop();
+      backend_state_ = BACKEND_STATE_INITIALIZED;
+      metrics::CastMetricsHelper::GetInstance()->RecordApplicationEvent(
+          "Cast.Platform.Ended");
+    }
 
     base::SingleThreadTaskRunner::GetCurrentDefault()->PostTask(
         FROM_HERE, std::move(pending_flush_task_->done_cb));