diff --git a/src/testdir/test_options.vim b/src/testdir/test_options.vim
index 70570cf..834ca44 100644
--- a/src/testdir/test_options.vim
+++ b/src/testdir/test_options.vim
@@ -272,6 +272,14 @@
   call feedkeys("i\<C-N>\<Esc>", 'xt')
   bwipe!
   call assert_fails('set complete=ix', 'E535:')
+  call assert_fails('set complete=x', 'E539:')
+  call assert_fails('set complete=..', 'E535:')
+  set complete=.,w,b,u,k,\ s,i,d,],t,U,f,o
+  set complete=.
+  set complete+=ffuncref('foo'\\,\ [10])
+  set complete=ffuncref('foo'\\,\ [10])
+  set complete&
+  set complete+=ffunction('foo'\\,\ [10\\,\ 20])
   set complete&
 endfun