diff --git a/src/unix/newlib/mod.rs b/src/unix/newlib/mod.rs
index 00b23a9a8664d..ce84f1421f0ea 100644
--- a/src/unix/newlib/mod.rs
+++ b/src/unix/newlib/mod.rs
@@ -234,11 +234,11 @@ s! {
     }
 
     pub struct pthread_attr_t { // Unverified
-        __size: [u64; __SIZEOF_PTHREAD_ATTR_T]
+        __size: [u8; __SIZEOF_PTHREAD_ATTR_T]
     }
 
     pub struct pthread_rwlockattr_t { // Unverified
-        __size: [u64; __SIZEOF_PTHREAD_RWLOCKATTR_T]
+        __size: [u8; __SIZEOF_PTHREAD_RWLOCKATTR_T]
     }
 }