diff --git a/js/xpconnect/src/xpcpublic.h b/js/xpconnect/src/xpcpublic.h
index dfc609a965d..3a92952768e 100644
--- a/js/xpconnect/src/xpcpublic.h
+++ b/js/xpconnect/src/xpcpublic.h
@@ -79,7 +79,7 @@ struct RuntimeStats;
 #define XPCONNECT_GLOBAL_FLAGS                                                \
     JSCLASS_DOM_GLOBAL | JSCLASS_HAS_PRIVATE |                                \
     JSCLASS_PRIVATE_IS_NSISUPPORTS | JSCLASS_IMPLEMENTS_BARRIERS |            \
-    JSCLASS_GLOBAL_FLAGS_WITH_SLOTS(2)
+    JSCLASS_GLOBAL_FLAGS_WITH_SLOTS(1)
 
 void
 TraceXPCGlobal(JSTracer *trc, JSObject *obj);