diff --git a/jsapi.rs b/jsapi.rs
index 0a858a06c..3e12201b2 100644
--- a/jsapi.rs
+++ b/jsapi.rs
@@ -396,7 +396,9 @@ pub type JSCSPEvalChecker = *u8;
 
 pub type JSWrapObjectCallback = *u8;
 
-pub type JSPreWrapCallback = *u8;
+pub type JSPreWrapCallback =
+    Option<extern "C" fn(cx: *mut JSContext, scope: *mut JSObject,
+                         object: *mut JSObject, flags: c_uint) -> *mut JSObject>;
 
 pub type JSSameCompartmentWrapObjectCallback = extern "C" fn(*JSContext, *JSObject) -> *JSObject;
 
diff --git a/jsfriendapi.rs b/jsfriendapi.rs
index 3b0f30caa..74bbdef06 100644
--- a/jsfriendapi.rs
+++ b/jsfriendapi.rs
@@ -2,6 +2,8 @@
  * 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 jsapi::{JSContext, JSObject};
+
 pub type JSJitPropertyOp = *u8;
 
 pub struct JSJitInfo {
@@ -12,6 +14,11 @@ pub struct JSJitInfo {
     pub isConstant: bool
 }
 
+extern {
+pub fn JS_ObjectToOuterObject(cx: *mut JSContext,
+                              obj: *mut JSObject) -> *mut JSObject;
+}
+
 //pub type JSJitInfo = JSJitInfo_struct;
 
 #[nolink]