diff --git a/changelog.d/17211.misc b/changelog.d/17211.misc
new file mode 100644
index 00000000000..144db03a409
--- /dev/null
+++ b/changelog.d/17211.misc
@@ -0,0 +1 @@
+Reduce work of calculating outbound device lists updates.
diff --git a/synapse/handlers/device.py b/synapse/handlers/device.py
index 55842e7c7b1..0432d97109a 100644
--- a/synapse/handlers/device.py
+++ b/synapse/handlers/device.py
@@ -906,6 +906,13 @@ async def _handle_new_device_update_async(self) -> None:
                         context=opentracing_context,
                     )
 
+                    await self.store.mark_redundant_device_lists_pokes(
+                        user_id=user_id,
+                        device_id=device_id,
+                        room_id=room_id,
+                        converted_upto_stream_id=stream_id,
+                    )
+
                     # Notify replication that we've updated the device list stream.
                     self.notifier.notify_replication()
 
diff --git a/synapse/storage/databases/main/devices.py b/synapse/storage/databases/main/devices.py
index f4410b5c02e..48384e238c1 100644
--- a/synapse/storage/databases/main/devices.py
+++ b/synapse/storage/databases/main/devices.py
@@ -2161,6 +2161,30 @@ def _add_device_outbound_poke_to_stream_txn(
                 },
             )
 
+    async def mark_redundant_device_lists_pokes(
+        self,
+        user_id: str,
+        device_id: str,
+        room_id: str,
+        converted_upto_stream_id: int,
+    ) -> None:
+        """If we've calculated the outbound pokes for a given room/device list
+        update, mark any subsequent changes as already converted"""
+
+        sql = """
+            UPDATE device_lists_changes_in_room
+            SET converted_to_destinations = true
+            WHERE stream_id > ? AND user_id = ? AND device_id = ?
+                AND room_id = ? AND NOT converted_to_destinations
+        """
+
+        def mark_redundant_device_lists_pokes_txn(txn: LoggingTransaction) -> None:
+            txn.execute(sql, (converted_upto_stream_id, user_id, device_id, room_id))
+
+        return await self.db_pool.runInteraction(
+            "mark_redundant_device_lists_pokes", mark_redundant_device_lists_pokes_txn
+        )
+
     def _add_device_outbound_room_poke_txn(
         self,
         txn: LoggingTransaction,