diff --git a/runtime/ftplugin/diff.vim b/runtime/ftplugin/diff.vim
index 0464290..bf37d46 100644
--- a/runtime/ftplugin/diff.vim
+++ b/runtime/ftplugin/diff.vim
@@ -1,7 +1,7 @@
 " Vim filetype plugin file
 " Language:	Diff
 " Maintainer:	Bram Moolenaar <Bram@vim.org>
-" Last Change:	2020 Jul 18
+" Last Change:	2021 Nov 14
 
 " Only do this when not done yet for this buffer
 if exists("b:did_ftplugin")
@@ -9,10 +9,15 @@
 endif
 let b:did_ftplugin = 1
 
-let b:undo_ftplugin = "setl modeline<"
+let b:undo_ftplugin = "setl modeline< commentstring<"
 
 " Don't use modelines in a diff, they apply to the diffed file
 setlocal nomodeline
 
 " If there are comments they start with #
-let &commentstring = "# %s"
+let &l:commentstring = "# %s"
+
+if (has("gui_win32") || has("gui_gtk")) && !exists("b:browsefilter")
+  let b:browsefilter = "Diff Files (*.diff)\t*.diff\nPatch Files (*.patch)\t*.h\nAll Files (*.*)\t*.*\n"
+  let b:undo_ftplugin ..= " | unlet! b:browsefilter"
+endif