diff --git a/collects/typed-racket/optimizer/tool/mzc.rkt b/collects/typed-racket/optimizer/tool/mzc.rkt
index b6cf7c0075..956ea0e598 100644
--- a/collects/typed-racket/optimizer/tool/mzc.rkt
+++ b/collects/typed-racket/optimizer/tool/mzc.rkt
@@ -2,9 +2,9 @@
 
 ;;;; Processing of mzc inliner logs.
 
-(require "utilities.rkt"
-         typed-racket/optimizer/logging
-         unstable/syntax racket/match unstable/match racket/list racket/string)
+(require typed-racket/optimizer/logging
+         unstable/syntax racket/match unstable/match racket/list racket/string
+         unstable/list)
 
 (provide log-message-from-mzc-opt?
          mzc-opt-log-message->log-entry
diff --git a/collects/typed-racket/optimizer/tool/utilities.rkt b/collects/typed-racket/optimizer/tool/utilities.rkt
index 242ab3ad8a..ac26dcabc6 100644
--- a/collects/typed-racket/optimizer/tool/utilities.rkt
+++ b/collects/typed-racket/optimizer/tool/utilities.rkt
@@ -7,27 +7,3 @@
 (define (regexp-filter r log)
   (for/list ([l (in-list log)] #:when (regexp-match r l))
     l))
-
-;; (y y -> bool) (listof x) #:key (x -> y) -> (listof (listof x))
-;; groups together elements that are considered equal
-;; =? should be reflexive, transitive and commutative
-(define (group-by =? l #:key [key values])
-  (for/fold ([res '()]) ; list of lists
-      ([elt (in-list l)])
-    (let loop ([classes     res] ; "zipper" of the equivalence classes
-               [rev-classes '()])
-      (cond [(null? classes)
-             ;; did not find an equivalence class, create a new one
-             (cons (list elt) res)]
-            [(=? (key elt) (key (car (car classes))))
-             ;; found the equivalence class
-             (append rev-classes ; we keep what we skipped
-                     ;; we extend the current class
-                     (list (cons elt (car classes)))
-                     (cdr classes))] ; and add the rest
-            [else ; keep going
-             (loop (cdr classes)
-                   (cons (car classes) rev-classes))]))))
-;; TODO add to unstable/list, and add tests. here's one
-;; -> (group-by = '(1 2 1 2 54 2 5 43 7 2 643 1 2 0))
-;; '((0) (2 2 2 2 2) (7) (43) (5) (54) (643) (1 1 1))