diff --git a/src/testdir/test_vim9_cmd.vim b/src/testdir/test_vim9_cmd.vim
index 7ec43e9..49bb873 100644
--- a/src/testdir/test_vim9_cmd.vim
+++ b/src/testdir/test_vim9_cmd.vim
@@ -14,6 +14,7 @@
   END
   CheckScriptSuccess(lines)
   assert_fails('vim9cmd', 'E1164:')
+  assert_fails('vim9cmd echo "con" . "cat"', 'E15:')
 
   lines =<< trim END
       vim9script