diff --git a/collects/mzlib/private/contract-arrow.ss b/collects/mzlib/private/contract-arrow.ss
index 2e9bbdc15a..7cba82ab28 100644
--- a/collects/mzlib/private/contract-arrow.ss
+++ b/collects/mzlib/private/contract-arrow.ss
@@ -23,6 +23,7 @@
            case->
 	   opt->
            opt->*
+           unconstrained-domain->
            object-contract
            mixin-contract
            make-mixin-contract
@@ -33,6 +34,31 @@
            check-procedure)
   
   
+  (define-syntax (unconstrained-domain-> stx)
+    (syntax-case stx ()
+      [(_ rngs ...)
+       (with-syntax ([(rngs-x ...) (generate-temporaries #'(rngs ...))]
+                     [(proj-x ...) (generate-temporaries #'(rngs ...))]
+                     [(p-app-x ...) (generate-temporaries #'(rngs ...))]
+                     [(res-x ...) (generate-temporaries #'(rngs ...))])
+         #'(let ([rngs-x (coerce-contract 'unconstrained-domain-> rngs)] ...)
+             (let ([proj-x ((proj-get rngs-x) rngs-x)] ...)
+               (make-proj-contract
+                (build-compound-type-name 'unconstrained-domain-> ((name-get rngs-x) rngs-x) ...)
+                (λ (pos-blame neg-blame src-info orig-str)
+                  (let ([p-app-x (proj-x pos-blame neg-blame src-info orig-str)] ...)
+                    (λ (val)
+                      (if (procedure? val)
+                          (λ args
+                            (let-values ([(res-x ...) (apply val args)])
+                              (values (p-app-x res-x) ...)))
+                          (raise-contract-error val
+                                                src-info
+                                                pos-blame
+                                                orig-str
+                                                "expected a procedure")))))
+                procedure?))))]))
+  
   (define-syntax (any stx)
     (raise-syntax-error 'any "Use any out of an arrow contract" stx))
 
diff --git a/collects/tests/mzscheme/contract-test.ss b/collects/tests/mzscheme/contract-test.ss
index e85e42b598..a1cf55d5c1 100644
--- a/collects/tests/mzscheme/contract-test.ss
+++ b/collects/tests/mzscheme/contract-test.ss
@@ -173,6 +173,9 @@
   (test/no-error '(opt->* (integer?) (integer?) any))
   (test/no-error '(opt->* ((flat-contract integer?)) ((flat-contract integer?)) any))
   
+  (test/no-error '(unconstrained-domain-> number?))
+  (test/no-error '(unconstrained-domain-> (flat-contract number?)))
+  
   (test/no-error '(listof any/c))
   (test/no-error '(listof (lambda (x) #t)))
   
@@ -1377,6 +1380,31 @@
                         'neg)])
       (cf (lambda (x%) 'going-to-be-bad))))   
 
+  (test/spec-passed
+   'unconstrained-domain->1
+   '(contract (unconstrained-domain-> number?) (λ (x) x) 'pos 'neg))
+  (test/pos-blame
+   'unconstrained-domain->2
+   '(contract (unconstrained-domain-> number?) 1 'pos 'neg))
+  (test/spec-passed
+   'unconstrained-domain->3
+   '((contract (unconstrained-domain-> number?) (λ (x) x) 'pos 'neg) 1))
+  (test/pos-blame
+   'unconstrained-domain->4
+   '((contract (unconstrained-domain-> number?) (λ (x) x) 'pos 'neg) #f))
+  
+  (test/spec-passed/result
+   'unconstrained-domain->4
+   '((contract (->r ([size natural-number/c]
+                     [proc (and/c (unconstrained-domain-> number?)
+                                  (λ (p) (procedure-arity-includes? p size)))])
+                    number?)
+               (λ (i f) (apply f (build-list i add1)))
+               'pos
+               'neg)
+     10 +)
+   55)
+  
   (test/pos-blame
    'or/c1
    '(contract (or/c false/c) #t 'pos 'neg))
@@ -4054,6 +4082,8 @@ so that propagation occurs.
   
   (test-name '(case-> (-> integer? integer?) (-> integer? integer? integer?))
              (case-> (-> integer? integer?) (-> integer? integer? integer?)))
+
+  (test-name '(unconstrained-domain-> number?) (unconstrained-domain-> number?))
   
   (test-name '(or/c) (or/c))
   (test-name '(or/c integer? gt0?) (or/c integer? (let ([gt0? (lambda (x) (> x 0))]) gt0?)))