diff --git a/utils.rkt b/utils.rkt
index e29c6e7..af0dc9d 100644
--- a/utils.rkt
+++ b/utils.rkt
@@ -25,7 +25,7 @@
                                    #:e-func (-> any/c any/c))
                                   graph?)]
                [pretty-print-set (-> generic-set? string?)]
-               [collect-by-key (-> (listof any/c) (listof any/c) (values (listof any/c) (listof any/c)))]
+               [collect-by-key (-> (listof any/c) (listof any/c) (values (listof any/c) (listof (listof any/c))))]
                [collect-by-key/sets (-> (listof any/c) (listof any/c) (values (listof any/c) (listof (set/c any/c))))]
 
                [ht-values:list->set (-> (hash/c any/c (listof any/c)) (hash/c any/c (set/c any/c)))])