From ba7eaddad2b98ac898016624ca47ba43b63c7f0a Mon Sep 17 00:00:00 2001
From: "Richard M. Stallman" <rms@gnu.org>
Date: Wed, 20 May 1998 00:40:19 +0000
Subject: [PATCH] (frame-background-mode): Define a :set function to update the
 background mode of existing frames.

---
 lisp/faces.el | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/lisp/faces.el b/lisp/faces.el
index 58b984ce876..2e3529fabf3 100644
--- a/lisp/faces.el
+++ b/lisp/faces.el
@@ -1432,6 +1432,10 @@ Set this to the symbol dark if your background color is dark, light if
 your background is light, or nil (default) if you want Emacs to
 examine the brightness for you."
   :group 'faces
+  :set #'(lambda (var value)
+	   (set var value)
+	   (mapcar 'frame-set-background-mode (frame-list)))
+  :initialize 'custom-initialize-changed
   :type '(choice (choice-item dark) 
 		 (choice-item light)
 		 (choice-item :tag "default" nil)))
-- 
2.39.2