--- a/dom/base/nsDOMClassInfo.cpp
+++ b/dom/base/nsDOMClassInfo.cpp
@@ -6763,16 +6763,17 @@ nsWindowSH::GlobalResolve(nsGlobalWindow
 
     JSObject *class_obj;
     holder->GetJSObject(&class_obj);
     NS_ASSERTION(class_obj, "The return value lied");
 
     // ... and define the constants from the DOM interface on that
     // constructor object.
 
+    JSAutoCompartment ac(cx, class_obj);
     rv = DefineInterfaceConstants(cx, class_obj, &name_struct->mIID);
     NS_ENSURE_SUCCESS(rv, rv);
 
     *did_resolve = true;
 
     return NS_OK;
   }