diff --git a/runtime/ftplugin/html.vim b/runtime/ftplugin/html.vim
index 7736b5b054..26b99d2bc3 100644
--- a/runtime/ftplugin/html.vim
+++ b/runtime/ftplugin/html.vim
@@ -2,9 +2,7 @@
 " Language:		HTML
 " Maintainer:		Doug Kearns <dougkearns@gmail.com>
 " Previous Maintainer:	Dan Sharp
-" Last Change:		2024 Jan 14
-" 2024 May 24 update 'commentstring' option
-" 2025 May 10 add expression folding #17141
+" Last Change:		2025 Sep 12
 
 if exists("b:did_ftplugin")
   finish
@@ -18,7 +16,12 @@ setlocal matchpairs+=<:>
 setlocal commentstring=<!--\ %s\ -->
 setlocal comments=s:<!--,m:\ \ \ \ ,e:-->
 
-let b:undo_ftplugin = "setlocal comments< commentstring< matchpairs<"
+if exists('b:undo_ftplugin')
+  " no whitespace before |, handle possible :unmap at end of current value
+  let b:undo_ftplugin ..= "| setlocal comments< commentstring< matchpairs<"
+else
+  let b:undo_ftplugin = "setlocal comments< commentstring< matchpairs<"
+endif
 
 if get(g:, "ft_html_autocomment", 0)
   setlocal formatoptions-=t formatoptions+=croql