diff -r 000000000000 -r 6474c204b198 js/src/jsapi-tests/testCustomIterator.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jsapi-tests/testCustomIterator.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,83 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "js/Class.h"
+#include "jsapi-tests/tests.h"
+
+static int iterCount = 0;
+
+static bool
+IterNext(JSContext *cx, unsigned argc, jsval *vp)
+{
+    JS::CallArgs args = JS::CallArgsFromVp(argc, vp);
+    if (iterCount++ == 100)
+        return JS_ThrowStopIteration(cx);
+    args.rval().setInt32(iterCount);
+    return true;
+}
+
+static JSObject *
+IterHook(JSContext *cx, JS::HandleObject obj, bool keysonly)
+{
+    JS::RootedObject iterObj(cx, JS_NewObject(cx, nullptr, JS::NullPtr(), JS::NullPtr()));
+    if (!iterObj)
+        return nullptr;
+    if (!JS_DefineFunction(cx, iterObj, "next", IterNext, 0, 0))
+        return nullptr;
+    return iterObj;
+}
+
+const js::Class HasCustomIterClass = {
+    "HasCustomIter",
+    0,
+    JS_PropertyStub,
+    JS_DeletePropertyStub,
+    JS_PropertyStub,
+    JS_StrictPropertyStub,
+    JS_EnumerateStub,
+    JS_ResolveStub,
+    JS_ConvertStub,
+    nullptr,
+    nullptr, /* call */
+    nullptr, /* hasInstance */
+    nullptr, /* construct */
+    nullptr, /* mark */
+    JS_NULL_CLASS_SPEC,
+    {
+        nullptr,     /* outerObject */
+        nullptr,     /* innerObject */
+        IterHook,
+        false        /* isWrappedNative */
+    }
+};
+
+static bool
+IterClassConstructor(JSContext *cx, unsigned argc, jsval *vp)
+{
+    JS::CallArgs args = JS::CallArgsFromVp(argc, vp);
+    JSObject *obj = JS_NewObjectForConstructor(cx, Jsvalify(&HasCustomIterClass), args);
+    if (!obj)
+        return false;
+    args.rval().setObject(*obj);
+    return true;
+}
+
+BEGIN_TEST(testCustomIterator_bug612523)
+{
+    CHECK(JS_InitClass(cx, global, js::NullPtr(), Jsvalify(&HasCustomIterClass),
+                       IterClassConstructor, 0, nullptr, nullptr, nullptr, nullptr));
+
+    JS::RootedValue result(cx);
+    EVAL("var o = new HasCustomIter(); \n"
+         "var j = 0; \n"
+         "for (var i in o) { ++j; }; \n"
+         "j;", &result);
+
+    CHECK(JSVAL_IS_INT(result));
+    CHECK_EQUAL(JSVAL_TO_INT(result), 100);
+    CHECK_EQUAL(iterCount, 101);
+
+    return true;
+}
+END_TEST(testCustomIterator_bug612523)