diff --git a/src/testdir/test_vim9_builtin.vim b/src/testdir/test_vim9_builtin.vim
index 8a6af57..dcf6007 100644
--- a/src/testdir/test_vim9_builtin.vim
+++ b/src/testdir/test_vim9_builtin.vim
@@ -111,6 +111,13 @@
       l->add(123)
   END
   CheckScriptFailure(lines, 'E1012: Type mismatch; expected string but got number', 3)
+
+  lines =<< trim END
+      vim9script
+      var l: list<string>
+      l->add(123)
+  END
+  CheckScriptFailure(lines, 'E1012: Type mismatch; expected string but got number', 3)
 enddef
 
 def Test_add_blob()