diff --git a/src/testdir/test_vim9_script.vim b/src/testdir/test_vim9_script.vim
index d2f5feb..78ff44b 100644
--- a/src/testdir/test_vim9_script.vim
+++ b/src/testdir/test_vim9_script.vim
@@ -1880,6 +1880,8 @@
   CheckScriptFailure(['vim9script', 'c'], 'E1100:')
   CheckScriptFailure(['vim9script', 'i = 1'], 'E488:')
   CheckScriptFailure(['vim9script', 'i'], 'E1100:')
+  CheckScriptFailure(['vim9script', 'o = 1'], 'E1100:')
+  CheckScriptFailure(['vim9script', 'o'], 'E1100:')
   CheckScriptFailure(['vim9script', 't'], 'E1100:')
   CheckScriptFailure(['vim9script', 't = 1'], 'E1100:')
   CheckScriptFailure(['vim9script', 'x = 1'], 'E1100:')