diff --git a/dom/base/nsDOMWindowUtils.cpp b/dom/base/nsDOMWindowUtils.cpp
index 12cbf4139a2a..ff0e9c1c231a 100644
--- a/dom/base/nsDOMWindowUtils.cpp
+++ b/dom/base/nsDOMWindowUtils.cpp
@@ -2600,6 +2600,7 @@ nsDOMWindowUtils::FlushApzRepaints(bool* aOutResult)
       return NS_ERROR_UNEXPECTED;
     }
     wrbc->SendFlushApzRepaints();
+    *aOutResult = true;
     return NS_OK;
   }
   ShadowLayerForwarder* forwarder = manager->AsShadowForwarder();