diff -r 000000000000 -r 6474c204b198 js/src/jit-test/tests/proxy/testDirectProxyGetOwnPropertyNames4.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit-test/tests/proxy/testDirectProxyGetOwnPropertyNames4.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,10 @@
+load(libdir + "asserts.js");
+
+// Throw a TypeError if the trap reports the same property twice
+assertThrowsInstanceOf(function () {
+    Object.getOwnPropertyNames(new Proxy({}, {
+        getOwnPropertyNames: function (target) {
+            return [ 'foo', 'foo' ];
+        }
+    }));
+}, TypeError);