diff --git a/runtime/optwin.vim b/runtime/optwin.vim
index d8f07b7..128e92e 100644
--- a/runtime/optwin.vim
+++ b/runtime/optwin.vim
@@ -1,7 +1,7 @@
 " These commands create the option window.
 "
 " Maintainer:	Bram Moolenaar <Bram@vim.org>
-" Last Change:	2018 Feb 11
+" Last Change:	2018 Feb 27
 
 " If there already is an option window, jump to that one.
 let buf = bufnr('option-window')
@@ -122,11 +122,13 @@
 endfun
 
 " Reset 'title' and 'icon' to make it work faster.
+" Reset 'undolevels' to avoid undo'ing until the buffer is empty.
 let s:old_title = &title
 let s:old_icon = &icon
 let s:old_sc = &sc
 let s:old_ru = &ru
-set notitle noicon nosc noru
+let s:old_ul = &ul
+set notitle noicon nosc noru ul=-1
 
 " If the current window is a help window, try finding a non-help window.
 " Relies on syntax highlighting to be switched on.
@@ -756,7 +758,7 @@
 call <SID>Header("editing text")
 call append("$", "undolevels\tmaximum number of changes that can be undone")
 call append("$", "\t(global or local to buffer)")
-call append("$", " \tset ul=" . &ul)
+call append("$", " \tset ul=" . s:old_ul)
 call append("$", "undofile\tautomatically save and restore undo history")
 call <SID>BinOptionG("udf", &udf)
 call append("$", "undodir\tlist of directories for undo files")
@@ -1438,6 +1440,7 @@
 let &ru = s:old_ru
 let &sc = s:old_sc
 let &cpo = s:cpo_save
-unlet s:old_title s:old_icon s:old_ru s:old_sc s:cpo_save s:idx s:lnum
+let &ul = s:old_ul
+unlet s:old_title s:old_icon s:old_ru s:old_sc s:cpo_save s:idx s:lnum s:old_ul
 
 " vim: ts=8 sw=2 sts=2