diff --git a/src/testdir/test_vim9_builtin.vim b/src/testdir/test_vim9_builtin.vim
index 978ceb0..df9e8ec 100644
--- a/src/testdir/test_vim9_builtin.vim
+++ b/src/testdir/test_vim9_builtin.vim
@@ -78,6 +78,17 @@
 def Test_add()
   CheckDefAndScriptFailure(['add({}, 1)'], ['E1013: Argument 1: type mismatch, expected list<any> but got dict<unknown>', 'E1226: List or Blob required for argument 1'])
   CheckDefFailure(['add([1], "a")'], 'E1012: Type mismatch; expected number but got string')
+
+  var lines =<< trim END
+    vim9script
+    g:thelist = [1]
+    lockvar g:thelist
+    def TryChange()
+      g:thelist->add(2)
+    enddef
+    TryChange()
+  END
+  CheckScriptFailure(lines, 'E741:')
 enddef
 
 def Test_add_blob()