diff --git a/src/libstd/rand/os.rs b/src/libstd/rand/os.rs
index 2be4129883f..07ad08e1b3c 100644
--- a/src/libstd/rand/os.rs
+++ b/src/libstd/rand/os.rs
@@ -85,6 +85,7 @@ mod imp {
         marker: marker::NoCopy
     }
 
+    #[repr(C)]
     struct SecRandom;
 
     static kSecRandomDefault: *const SecRandom = 0 as *const SecRandom;