diff --git a/dom/workers/WorkerRunnable.cpp b/dom/workers/WorkerRunnable.cpp
index cd034b21fdd..da7e28493e0 100644
--- a/dom/workers/WorkerRunnable.cpp
+++ b/dom/workers/WorkerRunnable.cpp
@@ -399,9 +399,12 @@ NS_IMETHODIMP
 StopSyncLoopRunnable::Cancel()
 {
   nsresult rv = Run();
-  NS_ENSURE_SUCCESS(rv, rv);
+  NS_WARN_IF(NS_FAILED(rv));
 
-  return NS_OK;
+  nsresult rv2 = WorkerSyncRunnable::Cancel();
+  NS_WARN_IF(NS_FAILED(rv2));
+
+  return NS_FAILED(rv) ? rv : rv2;
 }
 
 bool