Index: simple.el
===================================================================
RCS file: /cvsroot/emacs/emacs/lisp/simple.el,v
retrieving revision 1.651
diff -u -r1.651 simple.el
--- simple.el	23 Jul 2004 11:52:03 -0000	1.651
+++ simple.el	25 Jul 2004 18:26:52 -0000
@@ -4304,6 +4304,8 @@
 of the differing parts is, by contrast, slightly highlighted."
   :group 'completion)
 
+(defvar completion-root-regexp "^/")
+
 (defun completion-setup-function ()
   (let ((mainbuf (current-buffer))
 	(mbuf-contents (minibuffer-contents)))
@@ -4332,7 +4334,7 @@
 		(with-current-buffer mainbuf
 		  (save-excursion
 		    (goto-char (point-max))
-		    (skip-chars-backward "^/")
+		    (skip-chars-backward completion-root-regexp)
 		    (- (point) (minibuffer-prompt-end)))))
 	;; Otherwise, in minibuffer, the whole input is being completed.
 	(if (minibufferp mainbuf)