diff --git a/CHANGES.md b/CHANGES.md
index 99e314c68dfe..3f0c5685ea20 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -1,3 +1,9 @@
+Removal warning
+---------------
+
+Note that this release deprecates the ability for appservices to call `POST /_matrix/client/r0/register`  without the body parameter `type`. Appservice developers should use a `type` value of `m.login.application_service` as per the spec. In future releases, calling this endpoint with an access token but
+without a valid type will fail.
+
 Synapse 1.29.0 (2021-03-08)
 ===========================
 
diff --git a/changelog.d/9559.removal b/changelog.d/9559.removal
new file mode 100644
index 000000000000..f97bf56dc03f
--- /dev/null
+++ b/changelog.d/9559.removal
@@ -0,0 +1 @@
+Registering an Application Service user without using the `m.login.application_service` login type will be unsupported in an upcoming Synapse release.