diff --git a/collects/redex/private/generate-term.rkt b/collects/redex/private/generate-term.rkt
index ba4634422a..6befebe3e9 100644
--- a/collects/redex/private/generate-term.rkt
+++ b/collects/redex/private/generate-term.rkt
@@ -441,7 +441,8 @@
                        (λ ()
                          (match (gen-proc)
                            [`(,jf-name (,trms (... ...)))
-                            `(,jf-name ,@trms)])))
+                            `(,jf-name ,@trms)]
+                           [#f #f])))
                    #`(make-jf-gen/proc 'jf/mf-id #,clauses lang-id 'pat size))))]
           [_
            (raise-syntax-error 'redex-generator 
diff --git a/collects/redex/tests/gen-test.rkt b/collects/redex/tests/gen-test.rkt
index 79d4d285e4..81fd9db06b 100644
--- a/collects/redex/tests/gen-test.rkt
+++ b/collects/redex/tests/gen-test.rkt
@@ -73,6 +73,9 @@
   (test-equal (generate-term nats #:satisfying (sum (s z) (s z) n) +inf.0)
               '(sum (s z) (s z) (s (s z))))
   
+  (test-equal (generate-term nats #:satisfying (sum z z (s z)) 5)
+              #f)
+  
   (for ([_ 100])
     (match (generate-term nats #:satisfying (sum n_1 n_2 n_3) 5)
       [`(sum ,l ,r ,res)