diff --git a/runtime/indent/dtd.vim b/runtime/indent/dtd.vim
index 30c06aa..c2b3c0c 100644
--- a/runtime/indent/dtd.vim
+++ b/runtime/indent/dtd.vim
@@ -1,12 +1,15 @@
 " Vim indent file
-" Language:    	    DTD (Document Type Definition for XML)
-" Previous Maintainer:  Nikolai Weibull <now@bitwi.se>
-" Latest Revision:      2011-07-08
+" Language:		DTD (Document Type Definition for XML)
+" Maintainer:		Doug Kearns <dougkearns@gmail.com>
+" Previous Maintainer:	Nikolai Weibull <now@bitwi.se>
+" Last Change:		24 Sep 2021
 
 setlocal indentexpr=GetDTDIndent()
 setlocal indentkeys=!^F,o,O,>
 setlocal nosmartindent
 
+let b:undo_indent = "setl inde< indk< si<"
+
 if exists("*GetDTDIndent")
   finish
 endif