diff --git a/collects/unstable/file.rkt b/collects/unstable/file.rkt
index 974f50e7cb..ab785ff45b 100644
--- a/collects/unstable/file.rkt
+++ b/collects/unstable/file.rkt
@@ -16,4 +16,4 @@
         (make-directory dir)))))
 
 (provide/contract
- [make-directory*/ignore-exists-exn (path-string? . -> . void)])
+ [make-directory*/ignore-exists-exn (path-string? . -> . void?)])