diff --git a/components/script/dom/bindings/trace.rs b/components/script/dom/bindings/trace.rs
index 67b8832efedd..f9d81ee210ba 100644
--- a/components/script/dom/bindings/trace.rs
+++ b/components/script/dom/bindings/trace.rs
@@ -156,7 +156,7 @@ impl<T: JSTraceable> JSTraceable for Rc<T> {
     }
 }
 
-impl<T: JSTraceable> JSTraceable for Box<T> {
+impl<T: JSTraceable + ?Sized> JSTraceable for Box<T> {
     fn trace(&self, trc: *mut JSTracer) {
         (**self).trace(trc)
     }
diff --git a/components/script/dom/mod.rs b/components/script/dom/mod.rs
index 3861e5123e14..24951c0c075f 100644
--- a/components/script/dom/mod.rs
+++ b/components/script/dom/mod.rs
@@ -374,6 +374,7 @@ pub mod popstateevent;
 pub mod processinginstruction;
 pub mod progressevent;
 pub mod promise;
+pub mod promisenativehandler;
 pub mod radionodelist;
 pub mod range;
 pub mod request;
diff --git a/components/script/dom/promise.rs b/components/script/dom/promise.rs
index c99ae69792c0..79490e0bc13c 100644
--- a/components/script/dom/promise.rs
+++ b/components/script/dom/promise.rs
@@ -4,6 +4,7 @@
 
 use dom::bindings::callback::CallbackContainer;
 use dom::bindings::codegen::Bindings::PromiseBinding::AnyCallback;
+use dom::bindings::conversions::root_from_object;
 use dom::bindings::error::Fallible;
 use dom::bindings::global::GlobalRef;
 use dom::bindings::reflector::{Reflectable, MutReflectable, Reflector};
@@ -82,7 +83,7 @@ impl Promise {
     pub fn maybe_resolve_native<T>(&self, cx: *mut JSContext, val: &T) where T: ToJSValConvertible {
         rooted!(in(cx) let mut v = UndefinedValue());
         unsafe {
-            val.to_jsval(cx, m.handle_mut());
+            val.to_jsval(cx, v.handle_mut());
         }
         self.maybe_resolve(cx, v.handle());
     }
@@ -102,7 +103,7 @@ impl Promise {
     pub fn maybe_reject_native<T>(&self, cx: *mut JSContext, val: &T) where T: ToJSValConvertible {
         rooted!(in(cx) let mut v = UndefinedValue());
         unsafe {
-            val.to_jsval(cx, m.handle_mut());
+            val.to_jsval(cx, v.handle_mut());
         }
         self.maybe_reject(cx, v.handle());
     }
@@ -143,6 +144,29 @@ impl Promise {
         }
         obj
     }
+
+    #[allow(unsafe_code)]
+    pub fn append_native_handler(&self, handler: &PromiseNativeHandler) {
+        let global = self.global();
+        let cx = global.r().get_cx();
+        rooted!(in(cx) let resolve_func =
+                create_native_handler_function(cx,
+                                               handler.reflector().get_jsobject(),
+                                               NativeHandlerTask::Resolve));
+
+        rooted!(in(cx) let reject_func =
+                create_native_handler_function(cx,
+                                               handler.reflector().get_jsobject(),
+                                               NativeHandlerTask::Reject));
+
+        unsafe {
+            let ok = AddPromiseReactions(cx,
+                                         self.promise_obj(),
+                                         resolve_func.handle(),
+                                         reject_func.handle());
+            assert!(ok);
+        }
+    }
 }
 
 #[allow(unsafe_code)]
@@ -151,3 +175,51 @@ unsafe extern fn do_nothing_promise_executor(_cx: *mut JSContext, argc: u32, vp:
     *args.rval() = UndefinedValue();
     true
 }
+
+const SLOT_NATIVEHANDLER: usize = 0;
+const SLOT_NATIVEHANDLER_TASK: usize = 1;
+
+#[derive(PartialEq)]
+enum NativeHandlerTask {
+    Resolve = 0,
+    Reject = 1,
+}
+
+#[allow(unsafe_code)]
+unsafe extern fn native_handler_callback(cx: *mut JSContext, argc: u32, vp: *mut JSVal) -> bool {
+    let args = CallArgs::from_vp(vp, argc);
+    rooted!(in(cx) let v = *GetFunctionNativeReserved(args.callee(), SLOT_NATIVEHANDLER));
+    assert!(v.get().is_object());
+
+    let handler = root_from_object::<PromiseNativeHandler>(v.to_object())
+        .ok().expect("unexpected value for native handler in promise native handler callback");
+
+    rooted!(in(cx) let v = *GetFunctionNativeReserved(args.callee(), SLOT_NATIVEHANDLER_TASK));
+    match v.to_int32() {
+        v if v == NativeHandlerTask::Resolve as i32 => handler.resolved_callback(cx, args.get(0)),
+        v if v == NativeHandlerTask::Reject as i32 => handler.rejected_callback(cx, args.get(0)),
+        _ => panic!("unexpected native handler task value"),
+    };
+
+    true
+}
+
+#[allow(unsafe_code)]
+fn create_native_handler_function(cx: *mut JSContext,
+                                  holder: HandleObject,
+                                  task: NativeHandlerTask) -> *mut JSObject {
+    unsafe {
+        let func = NewFunctionWithReserved(cx, Some(native_handler_callback), 1, 0, ptr::null());
+        assert!(!func.is_null());
+
+        rooted!(in(cx) let obj = JS_GetFunctionObject(func));
+        assert!(!obj.is_null());
+        SetFunctionNativeReserved(obj.get(),
+                                  SLOT_NATIVEHANDLER,
+                                  &ObjectValue(&**holder));
+        SetFunctionNativeReserved(obj.get(),
+                                  SLOT_NATIVEHANDLER_TASK,
+                                  &Int32Value(task as i32));
+        obj.get()
+    }
+}
diff --git a/components/script/dom/promisenativehandler.rs b/components/script/dom/promisenativehandler.rs
new file mode 100644
index 000000000000..603122556ef1
--- /dev/null
+++ b/components/script/dom/promisenativehandler.rs
@@ -0,0 +1,49 @@
+/* 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/. */
+
+use dom::bindings::codegen::Bindings::PromiseNativeHandlerBinding;
+use dom::bindings::global::GlobalRef;
+use dom::bindings::js::Root;
+use dom::bindings::reflector::{Reflector, reflect_dom_object};
+use dom::bindings::trace::JSTraceable;
+use heapsize::HeapSizeOf;
+use js::jsapi::{JSContext, HandleValue};
+
+pub trait Callback: JSTraceable + HeapSizeOf {
+    fn callback(&self, cx: *mut JSContext, v: HandleValue);
+}
+
+#[dom_struct]
+pub struct PromiseNativeHandler {
+    reflector: Reflector,
+    resolve: Option<Box<Callback>>,
+    reject: Option<Box<Callback>>,
+}
+
+impl PromiseNativeHandler {
+    pub fn new(global: GlobalRef,
+               resolve: Option<Box<Callback>>,
+               reject: Option<Box<Callback>>)
+               -> Root<PromiseNativeHandler> {
+        reflect_dom_object(box PromiseNativeHandler {
+            reflector: Reflector::new(),
+            resolve: resolve,
+            reject: reject,
+        }, global, PromiseNativeHandlerBinding::Wrap)
+    }
+
+    fn callback(callback: &Option<Box<Callback>>, cx: *mut JSContext, v: HandleValue) {
+        if let Some(ref callback) = *callback {
+            callback.callback(cx, v)
+        }
+    }
+
+    pub fn resolved_callback(&self, cx: *mut JSContext, v: HandleValue) {
+        PromiseNativeHandler::callback(&self.resolve, cx, v)
+    }
+
+    pub fn rejected_callback(&self, cx: *mut JSContext, v: HandleValue) {
+        PromiseNativeHandler::callback(&self.reject, cx, v)
+    }
+}
diff --git a/components/script/dom/webidls/PromiseNativeHandler.webidl b/components/script/dom/webidls/PromiseNativeHandler.webidl
new file mode 100644
index 000000000000..caa1692dfd37
--- /dev/null
+++ b/components/script/dom/webidls/PromiseNativeHandler.webidl
@@ -0,0 +1,13 @@
+/* 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/. */
+
+// This interface is entirely internal to Servo, and should not be accessible to
+// web pages.
+
+// Hack to allow us to have JS owning and properly tracing/CCing/etc a
+// PromiseNativeHandler.
+[NoInterfaceObject,
+ Exposed=(Window,Worker)]
+interface PromiseNativeHandler {
+};