diff --git a/collects/typed-scheme/private/base-env.ss b/collects/typed-scheme/private/base-env.ss
index 1598c709..27d7a009 100644
--- a/collects/typed-scheme/private/base-env.ss
+++ b/collects/typed-scheme/private/base-env.ss
@@ -488,7 +488,7 @@
                  (cl-> [((-HT a b) a) b]
                        [((-HT a b) a (-> c)) (Un b c)]
                        [((-HT a b) a c) (Un b c)]))]
-[hash-ref! (-poly (a b c)
+[hash-ref! (-poly (a b)
                   (cl-> [((-HT a b) a (-> b)) b]
                         [((-HT a b) a b) b]))]
 [hash-iterate-first (-poly (a b)