diff --git a/collects/scheme/generator.ss b/collects/scheme/generator.ss
index 79a5939be1..6ad3a93259 100644
--- a/collects/scheme/generator.ss
+++ b/collects/scheme/generator.ss
@@ -22,7 +22,8 @@
 ;;         r)))
 ;;   (lambda () (cont)))
 
-;; not using parameterization
+;; not using parameterization (old version, doesn't deal with multiple
+;; inputs/outputs as the one below)
 #;
 (define-syntax-rule (generator body0 body ...)
   (let ([tag (make-continuation-prompt-tag)])
@@ -51,7 +52,13 @@
 
 (define yield-tag (make-continuation-prompt-tag))
 
-(define-syntax-rule (generator body0 body ...)
+(define-syntax (generator stx)
+  (syntax-case stx ()
+    [(_ () body0 body ...) #'(generator-old body0 body ...)]
+    [_ (raise-syntax-error
+        'generator "must have a form of (generator () body ...)")]))
+
+(define-syntax-rule (generator-old body0 body ...)
   (let ([state 'fresh])
     (define (cont)
       (define (yielder . vs)
@@ -95,22 +102,23 @@
       (raise-type-error 'generator-state "generator" g))))
 
 (define-syntax-rule (infinite-generator body0 body ...)
-  (generator (let loop () body0 body ... (loop))))
+  (generator () (let loop () body0 body ... (loop))))
 
 (define stop-value (gensym))
 
 (define-sequence-syntax in-generator
   (syntax-rules ()
     [(_ body0 body ...)
-     (in-producer (generator body0 body ... stop-value) stop-value)])
+     (in-producer (generator () body0 body ... stop-value) stop-value)])
   (lambda (stx)
     (syntax-case stx ()
       [((id ...) (_ body0 body ...))
        #'[(id ...)
-          (in-producer (generator body0 body ... stop-value) stop-value)]])))
+          (in-producer (generator () body0 body ... stop-value)
+                       stop-value)]])))
 
 (define (sequence->generator sequence)
-  (generator (for ([i sequence]) (yield i))))
+  (generator () (for ([i sequence]) (yield i))))
 
 (define (sequence->repeated-generator sequence)
   (sequence->generator (in-cycle sequence)))
diff --git a/collects/tests/mzscheme/for.ss b/collects/tests/mzscheme/for.ss
index 1d61983e4d..3f9102c384 100644
--- a/collects/tests/mzscheme/for.ss
+++ b/collects/tests/mzscheme/for.ss
@@ -235,10 +235,10 @@
         (for/list ([x (in-generator (helper 0) (helper 1) (helper 2))])
                   x)))
 
-(let ([g (lambda () (generator (yield 1) (yield 2) (yield 3)))])
+(let ([g (lambda () (generator () (yield 1) (yield 2) (yield 3)))])
   (let ([g (g)]) (test '(1 2 3) list (g) (g) (g)))
   (let ([g (g)]) (test '(1 2 3 10 10) list (g) (g) (g) (g 10) (g)))
-  (let ([g (generator (yield (yield (yield 1))))])
+  (let ([g (generator () (yield (yield (yield 1))))])
     (test '(1 2 3 4 4 4) list (g) (g 2) (g 3) (g 4) (g) (g)))
   (let ([g (g)])
     (test '(fresh 1 suspended 2 suspended 3 suspended last done)
@@ -247,8 +247,8 @@
                (generator-state g) (g)
                (generator-state g) (g 'last)
                (generator-state g)))
-  (letrec ([g (generator (yield (generator-state g))
-                         (yield (generator-state g)))])
+  (letrec ([g (generator () (yield (generator-state g))
+                            (yield (generator-state g)))])
     (test '(fresh running suspended running suspended last done)
           list (generator-state g) (g)
                (generator-state g) (g)
@@ -257,8 +257,8 @@
 
 (let* ([helper (lambda (pred num)
                  (for ([i (in-range 0 3)]) (yield (pred (+ i num)))))]
-       [g1 (generator (helper odd? 1) (yield 'odd))]
-       [g2 (generator (helper even? 1) (yield 'even))])
+       [g1 (generator () (helper odd? 1) (yield 'odd))]
+       [g2 (generator () (helper even? 1) (yield 'even))])
   (test '(#t #f #f #t #t #f odd even) 'yield-helper
         (list (g1) (g2) (g1) (g2) (g1) (g2) (g1) (g2))))