diff --git a/Cargo.toml b/Cargo.toml
index 1f3f8e8..38f8b05 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -9,4 +9,4 @@ repository = "https://github.com/seanmonstar/num_cpus"
 
 
 [dependencies]
-libc = "*"
+libc = "0.1.7"
diff --git a/src/lib.rs b/src/lib.rs
index 7a57a0e..1d897aa 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -57,11 +57,17 @@ fn get_num_cpus() -> usize {
     cpus as usize
 }
 
-#[cfg(target_os= "linux")]
+#[cfg(
+    any(
+        target_os = "linux",
+        target_os = "nacl",
+        target_os = "macos",
+        target_os = "ios"
+    )
+)]
 fn get_num_cpus() -> usize {
-    //to-do: replace with libc::_SC_NPROCESSORS_ONLN once available
     unsafe {
-        libc::sysconf(84) as usize
+        libc::sysconf(libc::_SC_NPROCESSORS_ONLN) as usize
     }
 }
 
@@ -73,27 +79,6 @@ fn get_num_cpus() -> usize {
     }
 }
 
-#[cfg(target_os = "nacl")]
-fn get_num_cpus() -> usize {
-    //to-do: replace with libc::_SC_NPROCESSORS_ONLN once available
-    unsafe {
-        libc::sysconf(1) as usize
-    }
-}
-
-#[cfg(
-    any(
-        target_os = "macos",
-        target_os = "ios"
-    )
-)]
-fn get_num_cpus() -> usize {
-    //to-do: replace with libc::_SC_NPROCESSORS_ONLN once available
-    unsafe {
-        libc::sysconf(58) as usize
-    }
-}
-
 #[test]
 fn lower_bound() {
     assert!(get() > 0);