diff --git a/collects/mzlib/file.ss b/collects/mzlib/file.ss
index eca2e928c9..a794743bde 100644
--- a/collects/mzlib/file.ss
+++ b/collects/mzlib/file.ss
@@ -478,9 +478,13 @@
       (define (do-path path acc)
         (cond [(and (not follow-links?) (link-exists? path)) (f path 'link acc)]
               [(directory-exists? path)
-               (do-paths (map (lambda (p) (build-path path p))
-                              (directory-list path))
-                         (f path 'dir acc))]
+               (call-with-values (lambda () (f path 'dir acc))
+                 (lambda (acc . descend?)
+                   (if (if (pair? descend?) (car descend?) #t)
+                     (do-paths (map (lambda (p) (build-path path p))
+                                    (directory-list path))
+                               acc)
+                     acc)))]
               [(file-exists? path) (f path 'file acc)]
               [(link-exists? path) (f path 'link acc)] ; dangling links
               [else (error 'fold-files "path disappeared: ~e" path)]))