diff --git a/src/testdir/test_undo.vim b/src/testdir/test_undo.vim
index 4a534ae..12d835b 100644
--- a/src/testdir/test_undo.vim
+++ b/src/testdir/test_undo.vim
@@ -458,7 +458,7 @@
   " Test undofile() with 'undodir' set to a non-existing directory.
   call assert_equal('', 'Xundofoo'->undofile())
 
-  if isdirectory('/tmp')
+  if !has('win32') && isdirectory('/tmp')
     set undodir=/tmp
     if has('osx')
       call assert_equal('/tmp/%private%tmp%file', undofile('///tmp/file'))