diff --git a/src/testdir/test_tabpage.vim b/src/testdir/test_tabpage.vim
index 35c9fd0..80cc8e5 100644
--- a/src/testdir/test_tabpage.vim
+++ b/src/testdir/test_tabpage.vim
@@ -130,6 +130,8 @@
   1tabmove
   call assert_equal(2, tabpagenr())
 
+  call assert_fails('let t = tabpagenr("#")', 'E15:')
+  call assert_equal(0, tabpagewinnr(-1))
   call assert_fails("99tabmove", 'E16:')
   call assert_fails("+99tabmove", 'E16:')
   call assert_fails("-99tabmove", 'E16:')