diff --git a/racket/collects/racket/contract/private/collapsible-common.rkt b/racket/collects/racket/contract/private/collapsible-common.rkt
index 144617403f..6da76248fe 100644
--- a/racket/collects/racket/contract/private/collapsible-common.rkt
+++ b/racket/collects/racket/contract/private/collapsible-common.rkt
@@ -219,10 +219,7 @@
 (define (fast-append l1 l2)
   (if (null? l2)
     l1
-    (let fast-append ((l1 l1))
-      (if (null? l1)
-        l2
-        (cons (car l1) (fast-append (cdr l1)))))))
+    (append l1 l2)))
 
 ;; Assuming that merging is symmetric, ie old-can-merge? iff new-can-merge?
 ;; This is true of the current c-c implementation, but if it ever changes