diff --git a/js/src/jit-test/tests/basic/cross-global-for-in.js b/js/src/jit-test/tests/basic/cross-global-for-in.js
new file mode 100644
index 000000000000..3fd772052557
--- /dev/null
+++ b/js/src/jit-test/tests/basic/cross-global-for-in.js
@@ -0,0 +1,11 @@
+var global = newGlobal();
+
+var arrayIter = (new global.Array())[global.Symbol.iterator]();
+var ArrayIteratorPrototype = Object.getPrototypeOf(arrayIter);
+var arrayIterProtoBase = Object.getPrototypeOf(ArrayIteratorPrototype);
+var IteratorPrototype = arrayIterProtoBase;
+delete IteratorPrototype.next;
+
+var obj = global.eval('({a: 1})')
+for (var x in obj) {}
+assertEq(x, "a");
diff --git a/js/src/jsiter.cpp b/js/src/jsiter.cpp
index 643007b40c00..b9e833762c62 100644
--- a/js/src/jsiter.cpp
+++ b/js/src/jsiter.cpp
@@ -477,6 +477,8 @@ Compare(T* a, T* b, size_t c)
     return true;
 }
 
+static bool iterator_next(JSContext* cx, unsigned argc, Value* vp);
+
 static inline PropertyIteratorObject*
 NewPropertyIteratorObject(JSContext* cx, unsigned flags)
 {
@@ -500,13 +502,35 @@ NewPropertyIteratorObject(JSContext* cx, unsigned flags)
                                          GetInitialHeap(GenericObject, clasp), shape, group);
         if (!obj)
             return nullptr;
+
         PropertyIteratorObject* res = &obj->as<PropertyIteratorObject>();
 
         MOZ_ASSERT(res->numFixedSlots() == JSObject::ITER_CLASS_NFIXED_SLOTS);
         return res;
     }
 
-    return NewBuiltinClassInstance<PropertyIteratorObject>(cx);
+    Rooted<PropertyIteratorObject*> res(cx, NewBuiltinClassInstance<PropertyIteratorObject>(cx));
+    if (!res)
+        return nullptr;
+
+    if (flags == 0) {
+        // Redefine next as an own property. This ensure that deleting the
+        // next method on the prototype doesn't break cross-global for .. in.
+        // We don't have to do this for JSITER_ENUMERATE because that object always
+        // takes an optimized path.
+        RootedFunction next(cx, NewFunctionWithProto(cx, NullPtr(), iterator_next, 0,
+                                                     JSFunction::NATIVE_FUN, NullPtr(),
+                                                     HandlePropertyName(cx->names().next),
+                                                     NullPtr()));
+        if (!next)
+            return nullptr;
+
+        RootedValue value(cx, ObjectValue(*next));
+        if (!DefineProperty(cx, res, cx->names().next, value))
+            return nullptr;
+    }
+
+    return res;
 }
 
 NativeIterator*