diff --git a/racket/collects/syntax/id-set.rkt b/racket/collects/syntax/id-set.rkt
index 3ed3f2768d..1c34464509 100644
--- a/racket/collects/syntax/id-set.rkt
+++ b/racket/collects/syntax/id-set.rkt
@@ -81,23 +81,23 @@
   (lambda (s)
     (and (id-set? s) (idsettype? s) (mutability? s))))
 
-(define (id-set-contract-check idsettype mutability b s)
+(define (id-set-contract-check idsettype mutability b s neg-party)
   (unless (id-set? s)
-    (raise-blame-error b s "expected either a free or bound identifier set"))
+    (raise-blame-error b #:missing-party neg-party s "expected either a free or bound identifier set"))
   (case idsettype
     [(free)
      (unless (free-id-set? s)
-       (raise-blame-error b s "expected a free-identifier set"))]
+       (raise-blame-error b #:missing-party neg-party s "expected a free-identifier set"))]
     [(bound)
      (unless (bound-id-set? s)
-       (raise-blame-error b s "expected a bound-identifier set"))])
+       (raise-blame-error b #:missing-party neg-party s "expected a bound-identifier set"))])
   (case mutability
     [(mutable)
      (unless (mutable-id-set? s)
-       (raise-blame-error b s "expected a mutable id set"))]
+       (raise-blame-error b #:missing-party neg-party s "expected a mutable id set"))]
     [(immutable)
      (unless (immutable-id-set? s)
-       (raise-blame-error b s "expected an immutable id set"))]))
+       (raise-blame-error b #:missing-party neg-party s "expected an immutable id set"))]))
 
 (define (flat-id-set-contract-first-order ctc)
   (define set-passes? (id-set-contract-first-order ctc))