diff --git a/CHANGES.md b/CHANGES.md
index 5d4e80499e..dfdd8aa68a 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -1,3 +1,18 @@
+Synapse 1.21.0rc3 (2020-10-08)
+==============================
+
+Bugfixes
+--------
+
+- Fix duplication of events on high traffic servers, caused by PostgreSQL `could not serialize access due to concurrent update` errors. ([\#8456](https://github.com/matrix-org/synapse/issues/8456))
+
+
+Internal Changes
+----------------
+
+- Add Groovy Gorilla to the list of distributions we build `.deb`s for. ([\#8475](https://github.com/matrix-org/synapse/issues/8475))
+
+
 Synapse 1.21.0rc2 (2020-10-02)
 ==============================
 
diff --git a/changelog.d/8456.misc b/changelog.d/8456.misc
deleted file mode 100644
index ccd260069b..0000000000
--- a/changelog.d/8456.misc
+++ /dev/null
@@ -1 +0,0 @@
-Reduce number of serialization errors of `MultiWriterIdGenerator._update_table`.
diff --git a/changelog.d/8475.misc b/changelog.d/8475.misc
deleted file mode 100644
index 69bcb04097..0000000000
--- a/changelog.d/8475.misc
+++ /dev/null
@@ -1 +0,0 @@
-Add Groovy Gorilla to the list of distributions we build `.deb`s for.
diff --git a/synapse/__init__.py b/synapse/__init__.py
index 500558bbdf..a86dc07ddc 100644
--- a/synapse/__init__.py
+++ b/synapse/__init__.py
@@ -48,7 +48,7 @@ try:
 except ImportError:
     pass
 
-__version__ = "1.21.0rc2"
+__version__ = "1.21.0rc3"
 
 if bool(os.environ.get("SYNAPSE_TEST_PATCH_LOG_CONTEXTS", False)):
     # We import here so that we don't have to install a bunch of deps when