diff -r 000000000000 -r 6474c204b198 js/src/jit-test/tests/ion/bug779631.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit-test/tests/ion/bug779631.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,9 @@
+var flag = 0;
+var a = {};
+Object.defineProperty(a, "value", {set: function(x) {}});
+a.watch("value", function(){flag++;});
+
+for(var i = 0; i < 100; i++) {
+    a.value = i;
+    assertEq(flag, i+1);
+}