diff -r 000000000000 -r 6474c204b198 js/src/jit-test/tests/jaeger/in.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit-test/tests/jaeger/in.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,21 @@
+function f(arr, b) {
+    var res = "";
+    var a;
+    if (b)
+        a = arr;
+    for (var i=100; i>-200; i--) {
+        if (i in a) {
+            res += i;
+        }
+    }
+    return res;
+}
+
+assertEq(f([1, , 2, 3], true), "320");
+
+try {
+    f([1, , 2, 3], false);
+    assertEq(0, 1);
+} catch(e) {
+    assertEq(e instanceof TypeError, true);
+}