diff -r 000000000000 -r 6474c204b198 js/src/jit-test/tests/jaeger/bug742393.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit-test/tests/jaeger/bug742393.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,11 @@
+var global = 0;
+Object.defineProperty(Array.prototype, "2", {get: function() { return global++; }});
+
+function f() {
+    var a = [];
+    var b = [0, 1, , 3];
+    for (var i=0; i<100; i++)
+        var c = a.concat(b);
+    assertEq(c[2], 99);
+}
+f();