From 8f23a02a9ea1fbc4213cae5664dcb9bf6b5205f6 Mon Sep 17 00:00:00 2001
From: Eli Zaretskii <eliz@gnu.org>
Date: Sat, 7 Oct 2023 17:58:54 +0300
Subject: [PATCH] Fix updating process-mark position in 'set-process-buffer'

* src/process.c (update_process_mark): Update marker position only
if P's process-mark is not already associated with P's buffer.
(Bug#66313)
---
 src/process.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/process.c b/src/process.c
index 5f7408a9395..46e57c1a7c2 100644
--- a/src/process.c
+++ b/src/process.c
@@ -1273,7 +1273,8 @@ static void
 update_process_mark (struct Lisp_Process *p)
 {
   Lisp_Object buffer = p->buffer;
-  if (BUFFERP (buffer))
+  if (BUFFERP (buffer)
+      && XMARKER (p->mark)->buffer != XBUFFER (buffer))
     set_marker_both (p->mark, buffer,
 		     BUF_ZV (XBUFFER (buffer)),
 		     BUF_ZV_BYTE (XBUFFER (buffer)));
-- 
2.39.2