diff --git a/src/sandbox/legacy/sandbox.ts b/src/sandbox/legacy/sandbox.ts
index 0440f0c..8f5a586 100644
--- a/src/sandbox/legacy/sandbox.ts
+++ b/src/sandbox/legacy/sandbox.ts
@@ -124,7 +124,12 @@ export default class SingularProxySandbox implements SandBox {
       },
 
       getOwnPropertyDescriptor(_: Window, p: PropertyKey): PropertyDescriptor | undefined {
-        return Object.getOwnPropertyDescriptor(rawWindow, p);
+        const descriptor = Object.getOwnPropertyDescriptor(rawWindow, p);
+        // A property cannot be reported as non-configurable, if it does not exists as an own property of the target object
+        if (descriptor && !descriptor.configurable) {
+          descriptor.configurable = true;
+        }
+        return descriptor;
       },
     });