diff --git a/collects/typed-scheme/private/base-env.rkt b/collects/typed-scheme/private/base-env.rkt
index 0cab853a..84049dbd 100644
--- a/collects/typed-scheme/private/base-env.rkt
+++ b/collects/typed-scheme/private/base-env.rkt
@@ -116,7 +116,9 @@
 [newline (->opt [-Output-Port] -Void)]
 [not (-> Univ B)]
 [box (-poly (a) (a . -> . (-box a)))]
-[unbox (-poly (a) ((-box a) . -> . a))]
+[unbox (-poly (a) (cl->*                   
+                   ((-box a) . -> . a)
+                   ((make-BoxTop) . -> . Univ)))]
 [set-box! (-poly (a) ((-box a) a . -> . -Void))]
 [box? (make-pred-ty (make-BoxTop))]
 [cons? (make-pred-ty (-pair Univ Univ))]