diff -Naur vim-8.1.0551/runtime/defaults.vim vim-8.1.0551-p/runtime/defaults.vim
--- vim-8.1.0551/runtime/defaults.vim	2018-11-28 21:20:38.000000000 +0100
+++ vim-8.1.0551-p/runtime/defaults.vim	2018-11-29 09:41:23.071405206 +0100
@@ -133,3 +133,8 @@
   " compatible).
   set nolangremap
 endif
+
+if has('persistent_undo')
+  " Disable creation of an extra .foo.un~ file.
+  set noundofile
+endif