diff -r 000000000000 -r 6474c204b198 js/src/tests/js1_5/Regress/regress-503860.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/tests/js1_5/Regress/regress-503860.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,24 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/*
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/licenses/publicdomain/
+ * Contributor: Jason Orendorff
+ */
+
+//-----------------------------------------------------------------------------
+var BUGNUMBER = 503860;
+var summary = "Don't shadow a readonly or setter proto-property";
+var expect = "PASS";
+var actual = "FAIL";
+var a = {y: 1};
+
+function B(){}
+B.prototype.__defineSetter__('x', function setx(val) { actual = expect; });
+var b = new B;
+b.y = 1;
+
+var arr = [a, b];       // same shape prior to bug 497789 fix
+for (var obj of arr)
+    obj.x = 2;          // should call b's setter but doesn't
+
+reportCompare(expect, actual, summary);