diff -uNr emacs-23.0.95-orig/lisp/gnus/message.el emacs-23.0.95/lisp/gnus/message.el
--- emacs-23.0.95-orig/lisp/gnus/message.el	2009-02-19 08:36:50.000000000 +0900
+++ emacs-23.0.95/lisp/gnus/message.el	2009-07-28 11:49:41.000000000 +0900
@@ -7810,7 +7810,8 @@
 	;; For unknown reason, MIME-Version doesn't exist.
 	(when (re-search-forward "^MIME-Version:" nil t)
 	  (forward-line 1)
-	  (insert "Content-Type: text/plain; charset=us-ascii\n"))))))
+	  (insert "Content-Type: text/plain; charset=UTF-8\n")
+	  (insert "Content-Transfer-Encoding: 7bit\n"))))))
 
 (defun message-read-from-minibuffer (prompt &optional initial-contents)
   "Read from the minibuffer while providing abbrev expansion."