diff --git a/collects/typed-scheme/private/base-env.ss b/collects/typed-scheme/private/base-env.ss
index f314d2727e..d6f49abebd 100644
--- a/collects/typed-scheme/private/base-env.ss
+++ b/collects/typed-scheme/private/base-env.ss
@@ -550,6 +550,11 @@
 [last-pair (-poly (a) ((-mu x (Un a (-val '()) (-pair a x)))
                        . -> . 
                        (Un (-pair a a) (-pair a (-val '())))))]
+[remove-duplicates
+ (-poly (a)
+        (cl->*
+         ((-lst a) . -> . (-lst a))
+         ((-lst a) (a a . -> . Univ) . -> . (-lst a))))]
 
 ;; scheme/tcp
 [tcp-listener? (make-pred-ty -TCP-Listener)]