diff --git a/src/testdir/test_vim9_cmd.vim b/src/testdir/test_vim9_cmd.vim
index fc1354e..79f19f0 100644
--- a/src/testdir/test_vim9_cmd.vim
+++ b/src/testdir/test_vim9_cmd.vim
@@ -1737,6 +1737,15 @@
       UnLockIt()
   END
   v9.CheckScriptFailure(lines, 'E46', 1)
+
+  lines =<< trim END
+      def _()
+        s:0([], s:0)
+        lockv
+      enddef
+      defcomp
+  END
+  v9.CheckScriptFailure(lines, 'E179', 2)
 enddef
 
 def Test_substitute_expr()