diff --git a/turnstile/examples/stlc+cons.rkt b/turnstile/examples/stlc+cons.rkt
index 7763ddb..6033583 100644
--- a/turnstile/examples/stlc+cons.rkt
+++ b/turnstile/examples/stlc+cons.rkt
@@ -15,7 +15,7 @@
          reverse length list-ref member)
 
 (define-type-constructor List
-  #:arity >= 0
+  #:arity = 1
   #:arg-variances (λ (stx) (make-list (sub1 (stx-length stx)) covariant)))
 
 (define-typed-syntax nil
diff --git a/turnstile/examples/tests/rackunit-typechecking.rkt b/turnstile/examples/tests/rackunit-typechecking.rkt
index ea65511..24b4f47 100644
--- a/turnstile/examples/tests/rackunit-typechecking.rkt
+++ b/turnstile/examples/tests/rackunit-typechecking.rkt
@@ -76,21 +76,25 @@
             (if (attribute msg-pat)
                 (eval-syntax (datum->stx #'h (stx->datum #'msg-pat)))
                 (eval-syntax (datum->stx #'h `(add-escs ,(stx->datum #'vmsg)))))
-     #:when (with-check-info*
-             (list (make-check-expected (syntax-e #'msg))
-                   (make-check-expression (syntax->datum stx))
-                   (make-check-location (build-source-location-list stx))
-                   (make-check-name 'typecheck-fail)
-                   (make-check-params (list (syntax->datum #'e) (syntax-e #'msg))))
-             (λ ()
-               (check-exn
-                (λ (ex)
-                  (and (or (exn:fail? ex) (exn:test:check? ex))
-                       ; check err msg matches
-                       (regexp-match? (syntax-e #'msg) (exn-message ex))))
-                (λ ()
-                  (expand/df #'e)))))
-     #'(void)]))
+     #`(let-syntax ([chk (λ (_stx)
+                           (with-check-info*
+                            ;; Most of these are actually ignored by rackunit's define-check.
+                            (list (make-check-expected (syntax-e #'msg))
+                                  (make-check-expression (syntax->datum #'stx))
+                                  (make-check-location (build-source-location-list #'stx))
+                                  (make-check-name 'typecheck-fail)
+                                  (make-check-params (list (syntax->datum #'e) (syntax-e #'msg))))
+                            (λ ()
+                              #,(syntax/loc stx
+                                  (check-exn
+                                   (λ (ex)
+                                     (and (or (exn:fail? ex) (exn:test:check? ex))
+                                          ; check err msg matches
+                                          (regexp-match? (syntax-e #'msg) (exn-message ex))))
+                                   (λ ()
+                                     (expand/df #'e))))))
+                           #'(void))])
+         chk)]))
 
 (define-syntax (typecheck-fail/toplvl stx)
   (syntax-parse stx #:datum-literals (:)