diff --git a/src/web_accessible_resources/window.open-defuser.js b/src/web_accessible_resources/window.open-defuser.js
index 3c3d40b36..7c4dccb63 100644
--- a/src/web_accessible_resources/window.open-defuser.js
+++ b/src/web_accessible_resources/window.open-defuser.js
@@ -80,18 +80,32 @@
             const decoy = /\bobj\b/.test(arg3)
                 ? createDecoy('object', 'data', url)
                 : createDecoy('iframe', 'src', url);
-            let popup = decoy.contentWindow || decoy;
-            Object.defineProperty(popup, 'closed', { value: false });
+            let popup = decoy.contentWindow;
+            if ( typeof popup === 'object' && popup !== null ) {
+                Object.defineProperty(popup, 'closed', { value: false });
+            } else {
+                const noopFunc = (function(){}).bind(self);
+                popup = new Proxy(self, {
+                    get: function(target, prop) {
+                        if ( prop === 'closed' ) { return false; }
+                        const r = Reflect.get(...arguments);
+                        if ( typeof r === 'function' ) { return noopFunc; }
+                        return target[prop];
+                    },
+                    set: function() {
+                        return Reflect.set(...arguments);
+                    },
+                });
+            }
             if ( /\blog\b/.test(arg3) ) {
                 popup = new Proxy(popup, {
                     get: function(target, prop) {
                         log('window.open / get', prop, '===', target[prop]);
-                        if ( prop === 'closed' ) { return false; }
-                        return target[prop];
+                        return Reflect.get(...arguments);
                     },
                     set: function(target, prop, value) {
                         log('window.open / set', prop, '=', value);
-                        target[prop] = value;
+                        return Reflect.set(...arguments);
                     },
                 });
             }