diff --git a/lisp/dired-aux.el b/lisp/dired-aux.el
index bfc37c5cdef..8bda25e9e37 100644
--- a/lisp/dired-aux.el
+++ b/lisp/dired-aux.el
@@ -365,9 +365,17 @@ List has a form of (file-name full-file-name (attribute-list))."
 ;;;###autoload
 (defun dired-do-chmod (&optional arg)
   "Change the mode of the marked (or next ARG) files.
-Symbolic modes like `g+w' are allowed.
-Type M-n to pull the file attributes of the file at point
-into the minibuffer."
+Both octal numeric modes like `644' and symbolic modes like `g+w'
+are supported.  Type M-n to pull the file attributes of the file
+at point into the minibuffer.
+
+See Info node `(coreutils)File permissions' for more information.
+Alternatively, see the man page for \"chmod\", using the command
+\\[man] in Emacs.
+
+Note that on MS-Windows only the `w' (write) bit is meaningful:
+resetting it makes the file read-only.  Changing any other bit
+has no effect on MS-Windows."
   (interactive "P")
   (let* ((files (dired-get-marked-files t arg nil nil t))
 	 ;; The source of default file attributes is the file at point.