diff --git a/runtime/indent/tex.vim b/runtime/indent/tex.vim
index d356ba9..68d13fb 100644
--- a/runtime/indent/tex.vim
+++ b/runtime/indent/tex.vim
@@ -67,7 +67,8 @@
 "               2020/04/26 by Yichao Zhou <broken.zhou AT gmail.com>
 "               (*) Fix a bug related to \[ & \].  Thanks Manuel Boni for
 "               reporting.
-"
+"               2023/08/28 by Vim Project
+"               (*) Set b:undo_indent.
 " }}}
 
 " Document: {{{
@@ -167,6 +168,7 @@
 setlocal indentkeys&
 exec 'setlocal indentkeys+=[,(,{,),},],\&' . substitute(g:tex_items, '^\|\(\\|\)', ',=', 'g')
 let g:tex_items = '^\s*' . substitute(g:tex_items, '^\(\^\\s\*\)*', '', '')
+let b:undo_indent = "setlocal autoindent< indentexpr< indentkeys< smartindent<"
 " }}}
 
 function! GetTeXIndent() " {{{