diff --git a/doc/misc/ChangeLog b/doc/misc/ChangeLog
index d8346259c6f..68d6d3c8f00 100644
--- a/doc/misc/ChangeLog
+++ b/doc/misc/ChangeLog
@@ -1,3 +1,8 @@
+2010-09-20  Katsumi Yamaoka  <yamaoka@jpl.org>
+
+	* emacs-mime.texi (rfc2047): Update description for
+	rfc2047-encode-parameter.
+
 2010-09-13  Michael Albinus  <michael.albinus@gmx.de>
 
 	* tramp.texi (Inline methods): Remove "ssh1_old", "ssh2_old" and
diff --git a/doc/misc/emacs-mime.texi b/doc/misc/emacs-mime.texi
index 3e996e945fb..2a0e8569266 100644
--- a/doc/misc/emacs-mime.texi
+++ b/doc/misc/emacs-mime.texi
@@ -1469,21 +1469,9 @@ Decode a string and return the results.
 
 @item rfc2047-encode-parameter
 @findex rfc2047-encode-parameter
-Encode a parameter in the RFC2047-like style.  This is a replacement for
-the @code{rfc2231-encode-string} function.  @xref{rfc2231}.
-
-When attaching files as @acronym{MIME} parts, we should use the RFC2231
-encoding to specify the file names containing non-@acronym{ASCII}
-characters.  However, many mail softwares don't support it in practice
-and recipients won't be able to extract files with correct names.
-Instead, the RFC2047-like encoding is acceptable generally.  This
-function provides the very RFC2047-like encoding, resigning to such a
-regrettable trend.  To use it, put the following line in your
-@file{~/.gnus.el} file:
-
-@lisp
-(defalias 'mail-header-encode-parameter 'rfc2047-encode-parameter)
-@end lisp
+Encode a parameter in the RFC2047-like style.  This is a substitution
+for the @code{rfc2231-encode-string} function, that is the standard but
+many mailers don't support it.  @xref{rfc2231}.
 
 @end table
 
diff --git a/lisp/gnus/ChangeLog b/lisp/gnus/ChangeLog
index dd54343616b..b85618ae705 100644
--- a/lisp/gnus/ChangeLog
+++ b/lisp/gnus/ChangeLog
@@ -1,3 +1,7 @@
+2010-09-20  Katsumi Yamaoka  <yamaoka@jpl.org>
+
+	* rfc2047.el (rfc2047-encode-parameter): Doc fix.
+
 2010-09-20  Lars Magne Ingebrigtsen  <larsi@gnus.org>
 
 	* nnimap.el (nnimap-request-group): Don't select the imap buffer before
diff --git a/lisp/gnus/rfc2047.el b/lisp/gnus/rfc2047.el
index 628423050b9..4fd1086ace0 100644
--- a/lisp/gnus/rfc2047.el
+++ b/lisp/gnus/rfc2047.el
@@ -851,18 +851,8 @@ Point moves to the end of the region."
 
 (defun rfc2047-encode-parameter (param value)
   "Return and PARAM=VALUE string encoded in the RFC2047-like style.
-This is a replacement for the `rfc2231-encode-string' function.
-
-When attaching files as MIME parts, we should use the RFC2231 encoding
-to specify the file names containing non-ASCII characters.  However,
-many mail softwares don't support it in practice and recipients won't
-be able to extract files with correct names.  Instead, the RFC2047-like
-encoding is acceptable generally.  This function provides the very
-RFC2047-like encoding, resigning to such a regrettable trend.  To use
-it, put the following line in your ~/.gnus.el file:
-
-\(defalias 'mail-header-encode-parameter 'rfc2047-encode-parameter)
-"
+This is a substitution for the `rfc2231-encode-string' function, that
+is the standard but many mailers don't support it."
   (let ((rfc2047-encoding-type 'mime)
 	(rfc2047-encode-max-chars nil))
     (rfc2045-encode-string param (rfc2047-encode-string value))))