diff --git a/synapse/storage/schema/main/delta/73/04partial_join_details.sql b/synapse/storage/schema/main/delta/73/04partial_join_details.sql
new file mode 100644
index 000000000000..0d086ef69913
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+++ b/synapse/storage/schema/main/delta/73/04partial_join_details.sql
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+/* Copyright 2022 The Matrix.org Foundation C.I.C
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+-- To ensure we correctly notify other homeservers about device list changes from our
+-- users after a partial join transitions to a full join, we need to know when we began
+-- the partial join. For now it's sufficient to know the device_list stream_id at the
+-- time of the partial join, and the join event created for us during a partial join.
+--
+-- Both columns are nullable without defaults, for backwards compatibility.
+ALTER TABLE partial_state_rooms ADD COLUMN device_lists_stream_id BIGINT;
+ALTER TABLE partial_state_rooms ADD COLUMN join_event_id TEXT REFERENCES events(event_id);