diff --git a/src/sem.rs b/src/sem.rs
index 22a462f..6f5c0f8 100644
--- a/src/sem.rs
+++ b/src/sem.rs
@@ -1,3 +1,5 @@
+use std::os::raw::c_long;
+
 use ffi::*;
 use {IntoTimeout, WaitTimeout};
 
@@ -18,7 +20,7 @@ impl Semaphore {
     /// Passing a value greater than zero is useful for managing a finite pool of resources,
     /// where the pool size is equal to the value.
     pub fn new(n: u64) -> Self {
-        let ptr = unsafe { dispatch_semaphore_create(n as i64) };
+        let ptr = unsafe { dispatch_semaphore_create(n as c_long) };
 
         Semaphore { ptr }
     }