diff -r 000000000000 -r 6474c204b198 js/src/jit-test/tests/debug/Object-defineProperty-12.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit-test/tests/debug/Object-defineProperty-12.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,18 @@
+// obj.defineProperty redefining an existing property leaves unspecified attributes unchanged.
+
+var g = newGlobal();
+g.p = 1;
+var dbg = new Debugger;
+var gw = dbg.addDebuggee(g);
+
+gw.defineProperty("p", {value: 2});
+assertEq(g.p, 2);
+
+var desc = Object.getOwnPropertyDescriptor(g, "p");
+assertEq(desc.configurable, true);
+assertEq(desc.enumerable, true);
+assertEq(desc.writable, true);
+assertEq(desc.value, 2);
+
+g.p = 3;
+assertEq(g.p, 3);