diff -r 000000000000 -r 6474c204b198 js/src/jit-test/tests/basic/testStringIncrement.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit-test/tests/basic/testStringIncrement.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,20 @@
+var a, b;
+
+function f(str) {
+    var n;
+    var k;
+    for (var i = 0; i < 18; ++i) {
+	n = str;
+	k = n++;
+	if (k) { }
+    }
+    return [k, n];
+}
+
+[a, b] = f("10");
+assertEq(a, 10);
+assertEq(b, 11);
+
+[a, b] = f("5");
+assertEq(a, 5);
+assertEq(b, 6);