diff --git a/src/code/unix.lisp b/src/code/unix.lisp
index 0f80e454e1a0c010a252a056d7726e5f4f38f001..2d056361150f7b3cdf3a1cf6b5db48ee104ffe33 100644
--- a/src/code/unix.lisp
+++ b/src/code/unix.lisp
@@ -40,6 +40,8 @@
 
 (def-alien-type int64-t (signed 64))
 
+(def-alien-type u-int64-t (unsigned 64))
+
 (def-alien-type ino-t
     #+netbsd u-int64-t
     #+alpha unsigned-int