diff --git a/CHANGELOG.md b/CHANGELOG.md
index b7a809834..37f4f4584 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,7 @@ BREAKING CHANGE
 ---------------
 
  * `MatrixClient::startClient` now returns a Promise. No method should be called on the client before that promise resolves. Before this method didn't return anything.
+ * A new `CATCHUP` sync state, emitted by `MatrixClient#"sync"` and returned by `MatrixClient::getSyncState()`, when doing initial sync after the `ERROR` state. See `MatrixClient` documentation for details.
 
 Changes in [0.11.0](https://github.com/matrix-org/matrix-js-sdk/releases/tag/v0.11.0) (TDB)
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