diff -r 000000000000 -r 6474c204b198 js/src/jit-test/tests/basic/testDecElem2.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit-test/tests/basic/testDecElem2.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,11 @@
+var obj = {s: ""};
+var name = "s";
+var a = [];
+for (var i = 0; i <= 13; i++) {
+    a[i] = 'x';
+    if (i > 8)
+        a[i] = --obj[name];  // first recording changes obj.s from string to number
+}
+assertEq(a.join(','), Array(10).join('x,') + '-1,-2,-3,-4,-5');
+assertEq(obj.s, -5);
+