diff --git a/racket/collects/racket/match/parse-helper.rkt b/racket/collects/racket/match/parse-helper.rkt
index b6ccec1cd9..5614f36a04 100644
--- a/racket/collects/racket/match/parse-helper.rkt
+++ b/racket/collects/racket/match/parse-helper.rkt
@@ -142,7 +142,7 @@
                                                (length ps)
                                                "missing fields"
                                                (list-tail
-                                                 (for/list [(i acc)]
+                                                 (for/list [(i (in-list acc))]
                                                            (symbol->string (syntax->datum i)))
                                                  (length ps)))
                                        stx pats)))