diff --git a/typed-racket-doc/typed-racket/scribblings/reference/types.scrbl b/typed-racket-doc/typed-racket/scribblings/reference/types.scrbl
index 80dc6f1f..5756424f 100644
--- a/typed-racket-doc/typed-racket/scribblings/reference/types.scrbl
+++ b/typed-racket-doc/typed-racket/scribblings/reference/types.scrbl
@@ -400,8 +400,8 @@ corresponding to @racket[trest], where @racket[bound]
 }
 
 @defform[(Setof t)]{is the type of a @rtech{hash set} of
-@racket[t]. This includes custom hash sets, but not sets that are
-implemented using @racket[gen:set].
+@racket[t]. This includes custom hash sets, but not mutable hash set
+or sets that are implemented using @racket[gen:set].
 @ex[(set 0 1 2 3)]
 @ex[(seteq 0 1 2 3)]
 }