diff --git a/src/libcore/sys.rs b/src/libcore/sys.rs
index 6515babcf6b7..76c0e9f0753e 100644
--- a/src/libcore/sys.rs
+++ b/src/libcore/sys.rs
@@ -105,17 +105,17 @@ class unlock {
 
 impl methods for lock_and_signal {
     unsafe fn lock<T>(f: fn() -> T) -> T {
-        rustrt::rust_lock_cond_lock(self.lock);
-        let _r = unlock(self.lock);
         do atomically {
+            rustrt::rust_lock_cond_lock(self.lock);
+            let _r = unlock(self.lock);
             f()
         }
     }
 
     unsafe fn lock_cond<T>(f: fn(condition) -> T) -> T {
-        rustrt::rust_lock_cond_lock(self.lock);
-        let _r = unlock(self.lock);
         do atomically {
+            rustrt::rust_lock_cond_lock(self.lock);
+            let _r = unlock(self.lock);
             f(condition_(self.lock))
         }
     }