diff --git a/src/testdir/test_autocmd.vim b/src/testdir/test_autocmd.vim
index 13febb0..eba365e 100644
--- a/src/testdir/test_autocmd.vim
+++ b/src/testdir/test_autocmd.vim
@@ -1157,6 +1157,7 @@
   call setline(1, ['buffer 2', 'line 2', 'line 3', 'line4'])
   call assert_fails(':diffthis', 'E788')
   call assert_equal(1, &diff)
+  set diffopt-=closeoff
   bw!
   call assert_fails(':diffoff!', 'E788')
   bw!