diff --git a/collects/mzlib/cm.ss b/collects/mzlib/cm.ss
index 268ed85..931ce71 100644
--- a/collects/mzlib/cm.ss
+++ b/collects/mzlib/cm.ss
@@ -90,7 +90,7 @@
        (lambda (op)
 	 (write (cons (version)
 		      (append (map path->main-collects-relative deps)
-			      (map (lambda (x) (path->main-collects-relative (cons 'ext x)))
+			      (map (lambda (x) (cons 'ext (path->main-collects-relative x)))
 				   external-deps)))
 		op)
 	 (newline op)))))
@@ -264,7 +264,12 @@
 				   (when (> t path-zo-time)
 				     (trace-printf "newer: ~a (~a > ~a)..." d t path-zo-time))
 				   (> t path-zo-time)))
-			       (map main-collects-relative->path (cdr deps)))
+			       (map (lambda (p)
+                                      (if (and (pair? p)
+                                               (eq? 'ext (car p)))
+                                          (cons 'ext (main-collects-relative->path (cdr p)))
+                                          (main-collects-relative->path p)))
+                                    (cdr deps)))
                         (compile-zo mode path))))))
                 (let ((stamp (get-compiled-time mode path #t)))
                   (hash-table-put! up-to-date path stamp)