diff --git a/collects/compiler/zo-marshal.rkt b/collects/compiler/zo-marshal.rkt
index e9403b252c..0e219725fb 100644
--- a/collects/compiler/zo-marshal.rkt
+++ b/collects/compiler/zo-marshal.rkt
@@ -970,7 +970,9 @@
      (let* ([l (protect-quote body)]
             [any-refs? (or (ormap (lambda (t) (memq t '(ref flonum))) param-types)
                            (ormap (lambda (t) (memq t '(flonum))) closure-types))]
-            [num-all-params ((if rest? add1 values) num-params)]
+            [num-all-params (if (and rest? (not (memq 'only-rest-arg-not-used flags)))
+                                (add1 num-params)
+                                num-params)]
             [l (cons (make-svector (if any-refs?
                                        (list->vector
                                         (append
diff --git a/collects/compiler/zo-parse.rkt b/collects/compiler/zo-parse.rkt
index e6e677700e..cf00f05ce9 100644
--- a/collects/compiler/zo-parse.rkt
+++ b/collects/compiler/zo-parse.rkt
@@ -117,8 +117,11 @@
                    (append
                     (if (zero? (bitwise-and flags flags CLOS_PRESERVES_MARKS)) null '(preserves-marks))
                     (if (zero? (bitwise-and flags flags CLOS_IS_METHOD)) null '(is-method))
-                    (if (zero? (bitwise-and flags flags CLOS_SINGLE_RESULT)) null '(single-result)))
-                   ((if rest? sub1 values) num-params)
+                    (if (zero? (bitwise-and flags flags CLOS_SINGLE_RESULT)) null '(single-result))
+                    (if (and rest? (zero? num-params)) '(only-rest-arg-not-used) null))
+                   (if (and rest? (num-params . > . 0))
+                       (sub1 num-params)
+                       num-params)
                    arg-types
                    rest?
                    (if (= closure-size (vector-length closed-over))
diff --git a/collects/compiler/zo-structs.rkt b/collects/compiler/zo-structs.rkt
index 4aba9f8ded..1e62a623d7 100644
--- a/collects/compiler/zo-structs.rkt
+++ b/collects/compiler/zo-structs.rkt
@@ -135,8 +135,8 @@
                                 [internal-context (or/c #f #t stx?)]))
 
 (define-form-struct (lam expr) ([name (or/c symbol? vector? empty?)]
-                                [flags (listof (or/c 'preserves-marks 'is-method 'single-result))]
-                                [num-params integer?] ; should be exact-nonnegative-integer?
+                                [flags (listof (or/c 'preserves-marks 'is-method 'single-result 'only-rest-arg-not-used))]
+                                [num-params exact-nonnegative-integer?]
                                 [param-types (listof (or/c 'val 'ref 'flonum))]
                                 [rest? boolean?]
                                 [closure-map (vectorof exact-nonnegative-integer?)]