diff -r 000000000000 -r 6474c204b198 js/src/jit-test/tests/ion/setelem-proto.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit-test/tests/ion/setelem-proto.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,26 @@
+var a = [1, 2, 3, 4];
+var count = 0;
+
+function f(arr, i) {
+    arr[2] = i;
+}
+
+for (var i=0; i<80; i++) {
+    f(a, i);
+    assertEq(a[2], i);
+}
+
+delete a[2];
+f(a, 50);
+assertEq(a[2], 50);
+
+Object.defineProperty(Object.prototype, "2", {
+    set: function() { count++; }
+});
+delete a[2];
+
+f(a, 100);
+f(a, 100);
+
+assertEq(a[2], undefined);
+assertEq(count, 2);