diff --git a/6-11/racket/collects/syntax/parse.rkt b/6-11/racket/collects/syntax/parse.rkt
index c28072d..6712f0f 100644
--- a/6-11/racket/collects/syntax/parse.rkt
+++ b/6-11/racket/collects/syntax/parse.rkt
@@ -25,7 +25,7 @@
   (require (only-in (for-template syntax/parse) pattern-expander))
   #;(define pattern-expander
     (let ()
-      #;(struct pattern-expander (proc) #:transparent
+      (struct pattern-expander (proc) #:transparent
         #:omit-define-syntaxes
         #:property prop:pattern-expander (λ (this) (pattern-expander-proc this)))
       pattern-expander)))
diff --git a/6-11/racket/collects/syntax/parse/private/runtime-reflect.rkt b/6-11/racket/collects/syntax/parse/private/runtime-reflect.rkt
index d561684..04d87f0 100644
--- a/6-11/racket/collects/syntax/parse/private/runtime-reflect.rkt
+++ b/6-11/racket/collects/syntax/parse/private/runtime-reflect.rkt
@@ -54,7 +54,9 @@ A Reified is
 (define (check-params who e-arity r-arity obj)
   (let ([e-pos (arity-minpos e-arity)]
         [e-kws (arity-minkws e-arity)])
-    (check-arity r-arity e-pos e-kws (lambda (msg) (error who "~a" msg)))))
+    (check-arity/neg r-arity e-pos e-kws
+                     (lambda (msg)
+                       (raise-mismatch-error who (string-append msg ": ") obj)))))
 
 (define (adapt-parser who esig0 rsig0 parser splicing?)
   (if (equal? esig0 rsig0)