diff --git a/federationapi/consumers/roomserver.go b/federationapi/consumers/roomserver.go
index ff2c8e5d4..c2c2d1874 100644
--- a/federationapi/consumers/roomserver.go
+++ b/federationapi/consumers/roomserver.go
@@ -146,28 +146,30 @@ func (s *OutputRoomEventConsumer) processInboundPeek(orp api.OutputNewInboundPee
 // processMessage updates the list of currently joined hosts in the room
 // and then sends the event to the hosts that were joined before the event.
 func (s *OutputRoomEventConsumer) processMessage(ore api.OutputNewRoomEvent) error {
-	eventsRes := &api.QueryEventsByIDResponse{}
-	if len(ore.AddsStateEventIDs) > 0 {
-		eventsReq := &api.QueryEventsByIDRequest{
-			EventIDs: ore.AddsStateEventIDs,
-		}
-		if err := s.rsAPI.QueryEventsByID(s.ctx, eventsReq, eventsRes); err != nil {
-			return fmt.Errorf("s.rsAPI.QueryEventsByID: %w", err)
-		}
-
-		found := false
-		for _, event := range eventsRes.Events {
-			if event.EventID() == ore.Event.EventID() {
-				found = true
-				break
-			}
-		}
-		if !found {
-			eventsRes.Events = append(eventsRes.Events, ore.Event)
+	addsStateEvents := []*gomatrixserverlib.HeaderedEvent{}
+	missingEventIDs := make([]string, 0, len(ore.AddsStateEventIDs))
+	for _, eventID := range ore.AddsStateEventIDs {
+		if eventID == ore.Event.EventID() {
+			addsStateEvents = append(addsStateEvents, ore.Event)
+		} else {
+			missingEventIDs = append(missingEventIDs, eventID)
 		}
 	}
 
-	addsJoinedHosts, err := joinedHostsFromEvents(gomatrixserverlib.UnwrapEventHeaders(eventsRes.Events))
+	// Ask the roomserver and add in the rest of the results into the set.
+	// Finally, work out if there are any more events missing.
+	if len(missingEventIDs) > 0 {
+		eventsReq := &api.QueryEventsByIDRequest{
+			EventIDs: missingEventIDs,
+		}
+		eventsRes := &api.QueryEventsByIDResponse{}
+		if err := s.rsAPI.QueryEventsByID(s.ctx, eventsReq, eventsRes); err != nil {
+			return fmt.Errorf("s.rsAPI.QueryEventsByID: %w", err)
+		}
+		addsStateEvents = append(addsStateEvents, eventsRes.Events...)
+	}
+
+	addsJoinedHosts, err := joinedHostsFromEvents(gomatrixserverlib.UnwrapEventHeaders(addsStateEvents))
 	if err != nil {
 		return err
 	}