diff --git a/dom/base/nsDOMClassInfo.cpp b/dom/base/nsDOMClassInfo.cpp
index ecc4a19f8c45..207fd953d84f 100644
--- a/dom/base/nsDOMClassInfo.cpp
+++ b/dom/base/nsDOMClassInfo.cpp
@@ -6541,6 +6541,7 @@ nsWindowSH::NewResolve(nsIXPConnectWrappedNative *wrapper, JSContext *cx,
                                       ::JS_GetStringLength(str), v, nsnull,
                                       nsnull,
                                       JSPROP_PERMANENT |
+                                      JSPROP_READONLY |
                                       JSPROP_ENUMERATE);
 
     if (!ok) {
@@ -8160,6 +8161,7 @@ nsDocumentSH::NewResolve(nsIXPConnectWrappedNative *wrapper, JSContext *cx,
                                       ::JS_GetStringLength(str), v, nsnull,
                                       nsnull,
                                       JSPROP_PERMANENT |
+                                      JSPROP_READONLY |
                                       JSPROP_ENUMERATE);
 
     if (!ok) {