diff --git a/dom/ipc/ContentChild.cpp b/dom/ipc/ContentChild.cpp
index 1a38404690..0fc3854e4d 100644
--- a/dom/ipc/ContentChild.cpp
+++ b/dom/ipc/ContentChild.cpp
@@ -2455,7 +2455,7 @@ ContentChild::RecvUpdateWindow(const uintptr_t& aChildId)
   if (parentInstance) {
   // sync! update call to the plugin instance that forces the
   // plugin to paint its child window.
-  parentInstance->CallUpdateWindow();
+  Unused << parentInstance->CallUpdateWindow();
   }
   return true;
 #else