diff --git a/runtime/indent/sdl.vim b/runtime/indent/sdl.vim
index 6ce30b6..40fe63f 100644
--- a/runtime/indent/sdl.vim
+++ b/runtime/indent/sdl.vim
@@ -1,7 +1,7 @@
 " Vim indent file
 " Language:	SDL
 " Maintainer:	Michael Piefel <entwurf@piefel.de>
-" Last Change:	10 December 2011
+" Last Change:	2021 Oct 03
 
 " Shamelessly stolen from the Vim-Script indent file
 
@@ -14,6 +14,8 @@
 setlocal indentexpr=GetSDLIndent()
 setlocal indentkeys+==~end,=~state,*<Return>
 
+let b:undo_indent = "setl inde< indk<"
+
 " Only define the function once.
 if exists("*GetSDLIndent")
 "  finish