diff --git a/src/testdir/test_tabpanel.vim b/src/testdir/test_tabpanel.vim
index 46ebe3b..e0a6a8c 100644
--- a/src/testdir/test_tabpanel.vim
+++ b/src/testdir/test_tabpanel.vim
@@ -529,6 +529,14 @@
   catch /^Vim\%((\a\+)\)\=:E117:/
   endtry
   call assert_true(empty(&tabpanel))
+
+  try
+    set tabpanel=%{my#util#TabPanelHighlight}%t
+    redraw!
+  catch /^Vim\%((\a\+)\)\=:E121:/
+  endtry
+  call assert_true(empty(&tabpanel))
+
   set tabpanel&vim
   set showtabpanel&vim
 endfunc