diff --git a/src/appkit.rs b/src/appkit.rs
index 008de23..db144f7 100644
--- a/src/appkit.rs
+++ b/src/appkit.rs
@@ -9,7 +9,7 @@
 
 #![allow(non_upper_case_globals)]
 
-use base::{id, msg_send, class, selector};
+use base::{id, msg_send, msg_send_stret, class, selector};
 use base::{SEL, NSInteger, NSUInteger};
 use libc;
 
@@ -272,6 +272,8 @@ pub enum NSEventModifierFlags {
     NSDeviceIndependentModifierFlagsMask    = 0xffff0000,
 }
 
+pub static NSMainMenuWindowLevel: libc::int32_t = 24;
+
 pub trait NSAutoreleasePool {
     unsafe fn new(_: Self) -> id {
         msg_send()(class("NSAutoreleasePool"), selector("new"))
@@ -927,3 +929,16 @@ impl NSEvent for id {
         msg_send()(self, selector("modifierFlags"))
     }
 }
+
+pub trait NSScreen {
+    unsafe fn mainScreen(_: Self) -> id {
+        msg_send()(class("NSScreen"), selector("mainScreen"))
+    }
+    unsafe fn frame(self) -> NSRect;
+}
+
+impl NSScreen for id {
+    unsafe fn frame(self) -> NSRect {
+        msg_send_stret()(self, selector("frame"))
+    }
+}
diff --git a/src/base.rs b/src/base.rs
index c7c0568..18cb03f 100644
--- a/src/base.rs
+++ b/src/base.rs
@@ -46,6 +46,7 @@ extern {
                                   -> Class;
     pub fn objc_getClass(name: *const libc::c_char) -> id;
     pub fn objc_msgSend(theReceiver: id, theSelector: SEL, ...) -> id;
+    pub fn objc_msgSend_stret(theReceiver: id, theSelector: SEL, ...);
     pub fn objc_registerClassPair(cls: Class);
     pub fn sel_registerName(name: *const libc::c_char) -> SEL;
 }
@@ -55,6 +56,10 @@ pub unsafe fn msg_send<T>() -> extern fn(theReceiver: id, theSelector: SEL, ...)
     mem::transmute(objc_msgSend)
 }
 
+pub unsafe fn msg_send_stret<T>() -> extern fn(theReceiver: id, theSelector: SEL, ...) -> T {
+    mem::transmute(objc_msgSend_stret)
+}
+
 /// A convenience method to convert the name of a class to the class object itself.
 #[inline]
 pub fn class(name: &str) -> id {