diff --git a/js/xpconnect/src/XPCConvert.cpp b/js/xpconnect/src/XPCConvert.cpp
index 40d7ada63cb21..c1c4f4ae4a2f4 100644
--- a/js/xpconnect/src/XPCConvert.cpp
+++ b/js/xpconnect/src/XPCConvert.cpp
@@ -53,9 +53,7 @@ using namespace JS;
 
 // static
 bool XPCConvert::GetISupportsFromJSObject(JSObject* obj, nsISupports** iface) {
-  const JSClass* jsclass = JS::GetClass(obj);
-  MOZ_ASSERT(jsclass, "obj has no class");
-  if (jsclass && jsclass->slot0IsISupports()) {
+  if (JS::GetClass(obj)->slot0IsISupports()) {
     *iface = JS::GetObjectISupports<nsISupports>(obj);
     return true;
   }