diff --git a/collects/redex/examples/delim-cont/model-impl.rkt b/collects/redex/examples/delim-cont/model-impl.rkt
index 8118d7668b..865288d05d 100644
--- a/collects/redex/examples/delim-cont/model-impl.rkt
+++ b/collects/redex/examples/delim-cont/model-impl.rkt
@@ -7,7 +7,8 @@
                      [_print print]
                      [_cons cons]
                      [_set! set!]
-                     [_zero? zero?]))
+                     [_zero? zero?])
+         (struct-out runtime-error) raise-runtime-error first-error)
 
 (define tag
   (let ([tags (make-hash)])
@@ -27,7 +28,7 @@
                  [(list? v) (andmap comparable? v)]
                  [else #t]))
          (tag v)
-         (raise-type-error '% "non-procedure" v)))
+         (raise-runtime-error '% "non-procedure" v)))
    (let ([h handler])
      (λ (x) (h x)))))
 
@@ -55,22 +56,31 @@
     (case v1
       [(#t) e2]
       [(#f) e3]
-      [else (raise-type-error 'if "#t or #f" v1)])))
+      [else (raise-runtime-error 'if "#t or #f" v1)])))
 
 (define (_+ x y) (+ x y))
 
 (define (_print n)
   (if (number? n)
       (begin (print n) #f)
-      (raise-type-error 'print "number" n)))
+      (raise-runtime-error 'print "number" n)))
 
 (define (_cons x xs)
   (if (list? xs)
       (cons x xs)
-      (raise-type-error 'cons "list?" 1 x xs)))
+      (raise-runtime-error 'cons "list?" xs)))
 
 (define-syntax-rule (_set! x e)
   (begin (set! x e) #f))
 
 (define (_zero? x)
-  (equal? 0 x))
\ No newline at end of file
+  (equal? 0 x))
+
+(define first-error (make-parameter #f))
+(struct runtime-error (primitive expected given) #:prefab)
+(define (raise-runtime-error . details)
+  (define error (apply runtime-error details))
+  (when (first-error)
+    (unless (unbox (first-error))
+      (set-box! (first-error) error)))
+  (raise error))
\ No newline at end of file
diff --git a/collects/redex/examples/delim-cont/randomized-tests.rkt b/collects/redex/examples/delim-cont/randomized-tests.rkt
index 775a76e515..ba1defdf72 100644
--- a/collects/redex/examples/delim-cont/randomized-tests.rkt
+++ b/collects/redex/examples/delim-cont/randomized-tests.rkt
@@ -2,6 +2,7 @@
 
 (require "grammar.ss" 
          "reduce.rkt"
+         (only-in "model-impl.rkt" runtime-error runtime-error?)
          (except-in redex/reduction-semantics plug)
          racket/runtime-path)
 
@@ -54,7 +55,13 @@
 (define impl-program
   (match-lambda
     [`(<> ,s [] ,e)
-     `(letrec ,s ,e)]
+     `(parameterize ([first-error (box #f)])
+        (define result
+          (with-handlers ([runtime-error? void])
+            (letrec ,s ,e)))
+        (match (first-error)
+          [(box #f) result]
+          [(box err) (raise err)]))]
     [e e]))
 
 (define-runtime-module-path model-impl "model-impl.rkt")
@@ -72,12 +79,12 @@
     (λ (test)
       (define output (open-output-string))
       (define result
-        (with-handlers ([exn:fail? 
-                         (λ (e)
-                           (match (exn-message e)
-                             [(regexp #rx"%: expected argument of type <non-procedure>")
-                              (bad-test "procedure as tag")]
-                             [_ (error e)]))])
+        (with-handlers ([exn:fail? (compose error exn-message)]
+                        [runtime-error?
+                         (match-lambda
+                           [(runtime-error '% "non-procedure" _)
+                            (bad-test "procedure as tag")]
+                           [e (error e)])])
           (parameterize ([current-output-port output])
             (eval test ns))))
       (if (or (error? result) (bad-test? result))