diff --git a/src/testdir/test_usercommands.vim b/src/testdir/test_usercommands.vim
index 00bbde4..2feeef0 100644
--- a/src/testdir/test_usercommands.vim
+++ b/src/testdir/test_usercommands.vim
@@ -798,4 +798,40 @@
   delcommand SubJapanesePeriodToDot
 endfunc
 
+" Declaring a variable in a {} uses Vim9 script rules, even when defined in a
+" legacy script.
+func Test_block_declaration_legacy_script()
+  let lines =<< trim END
+      command -range Rename {
+                     var save = @a
+                     @a = 'something'
+                     g:someExpr = @a
+                     @a = save
+                }
+  END
+  call writefile(lines, 'Xlegacy')
+  source Xlegacy
+
+  let lines =<< trim END
+      let @a = 'saved'
+      Rename
+      call assert_equal('something', g:someExpr)
+      call assert_equal('saved', @a)
+
+      let g:someExpr = 'xxx'
+      let @a = 'also'
+      Rename
+      call assert_equal('something', g:someExpr)
+      call assert_equal('also', @a)
+  END
+  call writefile(lines, 'Xother')
+  source Xother
+
+  unlet g:someExpr
+  call delete('Xlegacy')
+  call delete('Xother')
+  delcommand Rename
+endfunc
+
+
 " vim: shiftwidth=2 sts=2 expandtab