diff --git a/scribblings/utils.scrbl b/scribblings/utils.scrbl
index 7c98c60..9483e1a 100644
--- a/scribblings/utils.scrbl
+++ b/scribblings/utils.scrbl
@@ -327,8 +327,8 @@ unweighted graph.
 
 @section{Additional list and hash map utilities}
 
-@defproc[(collect-by-key [keys (Listof Any)] [vals (Listof Any)])
-			 (Values (Listof Any) (Listof (Listof Any)))]{
+@defproc[(collect-by-key [keys (Listof a)] [vals (Listof b)])
+			 (Values (Listof a) (Listof (Listof b)))]{
 
 Given a list of keys and the corresponding values, collects all the values
 associated to any given key and returns a list of keys without duplicates, and
@@ -341,8 +341,8 @@ produced by this function are suitable for graph constructors.
 (collect-by-key '(a b a) '(1 2 3))
 ]}
 
-@defproc[(collect-by-key/sets [keys (Listof Any)] [vals (Listof Any)])
-			      (Values (Listof Any) (Listof (Setof Any)))]{
+@defproc[(collect-by-key/sets [keys (Listof a)] [vals (Listof b)])
+			      (Values (Listof a) (Listof (Setof b)))]{
 
 Like @racket[collect-by-key], but produce a list of sets instead of a list
 of lists.
diff --git a/utils.rkt b/utils.rkt
index 5084f51..0436806 100644
--- a/utils.rkt
+++ b/utils.rkt
@@ -381,15 +381,15 @@
       (check-equal? (edge-weight new-gr3 'aa 'bb) 20)
       (check-equal? (edge-weight new-gr3 'bb 'cc) 22)))
 
-  (: collect-by-key (-> (Listof Any) (Listof Any)
-                        (Values (Listof Any) (Listof (Listof Any)))))
+  (: collect-by-key (All (a b) (-> (Listof a) (Listof b)
+                                   (Values (Listof a) (Listof (Listof b))))))
   (define (collect-by-key keys vals)
-    (for/fold ([ht : (HashTable Any (Listof Any))
+    (for/fold ([ht : (HashTable a (Listof b))
                    (make-immutable-hash)]
                #:result (values (hash-keys ht) (hash-values ht)))
               ([e keys]
                [l vals])
-      ((inst hash-update Any (Listof Any)) ht e (λ (ls) (cons l ls)) (λ () empty))))
+      ((inst hash-update a (Listof b)) ht e (λ (ls) (cons l ls)) (λ () empty))))
 
   (module+ test
     (test-case "collect-by-key"
@@ -398,11 +398,11 @@
       (check-equal? e1 '((1 2) (1 3))) (check-equal? l1 '((a) (b)))
       (check-equal? e2 '((1 2))) (check-equal? l2 '((b a)))))
 
-  (: collect-by-key/sets (-> (Listof Any) (Listof Any)
-                             (Values (Listof Any) (Listof (Setof Any)))))
+  (: collect-by-key/sets (All (a b) (-> (Listof a) (Listof b)
+                                        (Values (Listof a) (Listof (Setof b))))))
   (define (collect-by-key/sets edges labels)
     (define-values (es ls) (collect-by-key edges labels))
-    (values es ((inst map (Setof Any) (Listof Any)) list->set ls)))
+    (values es ((inst map (Setof b) (Listof b)) list->set ls)))
 
   (module+ test
     (test-case "collect-by-key/sets"