From 0aeb95fb07066636362bf109e8da98969e6667a3 Mon Sep 17 00:00:00 2001
From: Andrew Morgan <andrew@amorgan.xyz>
Date: Tue, 30 Sep 2025 12:05:28 +0100
Subject: [PATCH] Add MAS note to 1.139.0 changelog

---
 CHANGES.md | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/CHANGES.md b/CHANGES.md
index 9984efc99e..e8b04c419c 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -1,5 +1,15 @@
 # Synapse 1.139.0 (2025-09-30)
 
+### `/register` requests from old application service implementations may break when using MAS
+
+If you are using Matrix Authentication Service (MAS), as of this release any
+Application Services that do not set `inhibit_login=true` when calling `POST
+/_matrix/client/v3/register` will receive the error
+`IO.ELEMENT.MSC4190.M_APPSERVICE_LOGIN_UNSUPPORTED` in response. Please see [the
+upgrade
+notes](https://element-hq.github.io/synapse/develop/upgrade.html#register-requests-from-old-application-service-implementations-may-break-when-using-mas)
+for more information.
+
 No significant changes since 1.139.0rc3.