diff --git a/CHANGES.md b/CHANGES.md
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--- a/CHANGES.md
+++ b/CHANGES.md
@@ -7,7 +7,7 @@
 ### Bugfixes
 
 - Fix a rare bug introduced in v1.29.0 where invalidating a user's access token from a worker could raise an error. ([\#17779](https://github.com/element-hq/synapse/issues/17779))
-- In the response to `GET /_matrix/client/versions`, set the `unstable_features` flag for MSC4140 to `false` when server configuration disables support for delayed events. ([\#17780](https://github.com/element-hq/synapse/issues/17780))
+- In the response to `GET /_matrix/client/versions`, set the `unstable_features` flag for [MSC4140](https://github.com/matrix-org/matrix-spec-proposals/pull/4140) to `false` when server configuration disables support for delayed events. ([\#17780](https://github.com/element-hq/synapse/issues/17780))
 - Improve input validation and room membership checks in admin redaction API. ([\#17792](https://github.com/element-hq/synapse/issues/17792))
 
 ### Improved Documentation