diff --git a/lib/xmlhttprequest.js b/lib/xmlhttprequest.js
index 2b86a49..ba631bb 100644
--- a/lib/xmlhttprequest.js
+++ b/lib/xmlhttprequest.js
@@ -440,9 +440,10 @@ class XMLHttpRequest extends XMLHttpRequestEventTarget {
     upload: Object.assign({}, OVERRIDE_PROTECTION_DESCRIPTOR, {
       value: null
     }),
-    withCredentials: Object.assign({}, OVERRIDE_PROTECTION_DESCRIPTOR, {
-      value: false
-    })
+    withCredentials: {
+      value: false,
+      writable: true
+    }
   };
   Object.defineProperties(XMLHttpRequest, xmlHttpRequestConstants);
   Object.defineProperties(XMLHttpRequest.prototype, Object.assign(