diff --git a/roomserver/internal/input/input_events.go b/roomserver/internal/input/input_events.go
index 3ad4c202..4e0ff274 100644
--- a/roomserver/internal/input/input_events.go
+++ b/roomserver/internal/input/input_events.go
@@ -101,20 +101,27 @@ func (r *Inputer) processRoomEvent(
 
 	// First of all, check that the auth events of the event are known.
 	// If they aren't then we will ask the federation API for them.
-	if err := r.checkForMissingAuthEvents(ctx, input.Event, map[string]types.EventNID{}); err != nil {
-		logrus.WithError(err).Error("XXX: r.checkForMissingAuthEvents")
+	isRejected := false
+	authEvents := gomatrixserverlib.NewAuthEvents(nil)
+	knownAuthEvents := map[string]types.Event{}
+	if err := r.checkForMissingAuthEvents(ctx, input.Event, &authEvents, knownAuthEvents); err != nil {
 		return "", fmt.Errorf("r.checkForMissingAuthEvents: %w", err)
 	}
 
-	// Check that the event passes authentication checks and work out
-	// the numeric IDs for the auth events.
-	isRejected := false
-	authEventNIDs, rejectionErr := helpers.CheckAuthEvents(ctx, r.DB, headered, input.AuthEventIDs)
-	if rejectionErr != nil {
-		logrus.WithError(rejectionErr).WithField("event_id", event.EventID()).WithField("auth_event_ids", input.AuthEventIDs).Error("helpers.CheckAuthEvents failed for event, rejecting event")
+	// Check if the event is allowed by its auth events. If it isn't then
+	// we consider the event to be "rejected" — it will still be persisted.
+	var rejectionErr error
+	if rejectionErr = gomatrixserverlib.Allowed(event, &authEvents); rejectionErr != nil {
 		isRejected = true
 	}
 
+	// Accumulate the auth event NIDs.
+	authEventIDs := event.AuthEventIDs()
+	authEventNIDs := make([]types.EventNID, 0, len(authEventIDs))
+	for _, authEventID := range authEventIDs {
+		authEventNIDs = append(authEventNIDs, knownAuthEvents[authEventID].EventNID)
+	}
+
 	// Then check if the prev events are known, which we need in order
 	// to calculate the state before the event.
 	if err := r.checkForMissingPrevEvents(ctx, input); err != nil {
@@ -246,29 +253,32 @@ func (r *Inputer) processRoomEvent(
 func (r *Inputer) checkForMissingAuthEvents(
 	ctx context.Context,
 	event *gomatrixserverlib.HeaderedEvent,
-	cache map[string]types.EventNID,
+	auth *gomatrixserverlib.AuthEvents,
+	known map[string]types.Event,
 ) error {
 	authEventIDs := event.AuthEventIDs()
 	if len(authEventIDs) == 0 {
 		return nil
 	}
 
-	knownAuthEventNIDs, err := r.DB.EventNIDs(ctx, authEventIDs)
-	if err != nil {
-		return fmt.Errorf("r.DB.EventNIDs: %w", err)
-	}
-	for authEventID, authEventNID := range knownAuthEventNIDs {
-		cache[authEventID] = authEventNID
-	}
+	unknown := map[string]struct{}{}
 
-	missingAuthEventIDs := make([]string, 0, len(authEventIDs)-len(knownAuthEventNIDs))
-	for _, authEventID := range authEventIDs {
-		if _, ok := knownAuthEventNIDs[authEventID]; !ok {
-			missingAuthEventIDs = append(missingAuthEventIDs, authEventID)
+	authEvents, err := r.DB.EventsFromIDs(ctx, authEventIDs)
+	if err != nil {
+		return fmt.Errorf("r.DB.EventsFromIDs: %w", err)
+	}
+	for _, event := range authEvents {
+		if event.Event != nil {
+			known[event.EventID()] = event
+			if err := auth.AddEvent(event.Event); err != nil {
+				return fmt.Errorf("auth.AddEvent: %w", err)
+			}
+		} else {
+			unknown[event.EventID()] = struct{}{}
 		}
 	}
 
-	if len(missingAuthEventIDs) > 0 {
+	if len(unknown) > 0 {
 		req := &fedapi.QueryEventAuthFromFederationRequest{
 			RoomID:  event.RoomID(),
 			EventID: event.EventID(),
@@ -282,45 +292,40 @@ func (r *Inputer) checkForMissingAuthEvents(
 			res.Events,
 			gomatrixserverlib.TopologicalOrderByAuthEvents,
 		) {
-			// Work out which event NIDs we need to look up from the database. If
-			// the event NID is already in the event map in memory then we can don't
-			// need to ask the database again.
-			neededAuthEventNIDs := make([]string, 0, len(event.AuthEventIDs()))
-			for _, authEventID := range event.AuthEventIDs() {
-				if _, ok := cache[authEventID]; !ok {
-					neededAuthEventNIDs = append(neededAuthEventNIDs, authEventID)
-				}
+			// If we already know about this event then we don't need to store
+			// it or do anything further with it.
+			if _, ok := known[event.EventID()]; ok {
+				continue
 			}
 
-			// If we need to fetch some event NIDs from the database then do that.
-			// We will also add those to the auth event map in memory, so that we
-			// can skip future database hits for the same event IDs.
-			if len(neededAuthEventNIDs) > 0 {
-				newAuthEventNIDs, err := r.DB.EventNIDs(ctx, neededAuthEventNIDs)
-				if err != nil {
-					return fmt.Errorf("r.DB.EventNIDs: %w", err)
-				}
-				for authEventID, authEventNID := range newAuthEventNIDs {
-					cache[authEventID] = authEventNID
+			// Otherwise, we need to store, and that means we need to know the
+			// auth event NIDs. Let's see if we can find those.
+			authEventNIDs := make([]types.EventNID, 0, len(event.AuthEventIDs()))
+			for _, eventID := range event.AuthEventIDs() {
+				knownEvent, ok := known[eventID]
+				if !ok {
+					return fmt.Errorf("missing auth event %s for %s", eventID, event.EventID())
 				}
+				authEventNIDs = append(authEventNIDs, knownEvent.EventNID)
 			}
 
-			// Now collect the event NIDs for all of the auth events.
-			authEventNIDsForEvent := make([]types.EventNID, 0, len(event.AuthEventIDs()))
-			for _, authEventID := range event.AuthEventIDs() {
-				authEventNIDsForEvent = append(authEventNIDsForEvent, cache[authEventID])
-			}
-
-			// If we haven't accumulated all of the auth events needed for the
-			// event then we shouldn't persist the event as something is wrong.
-			if len(authEventNIDsForEvent) != len(event.AuthEventIDs()) {
-				return fmt.Errorf("missing auth event NIDs for event %s", event.EventID())
+			// Let's take a note of the fact that we now know about this event.
+			known[event.EventID()] = types.Event{}
+			if err := auth.AddEvent(event); err != nil {
+				return fmt.Errorf("auth.AddEvent: %w", err)
 			}
 
 			// Finally, store the event in the database.
-			if _, _, _, _, err := r.DB.StoreEvent(ctx, event, authEventNIDsForEvent, false); err != nil {
+			eventNID, _, _, _, _, err := r.DB.StoreEvent(ctx, event, authEventNIDs, false)
+			if err != nil {
 				return fmt.Errorf("r.DB.StoreEvent: %w", err)
 			}
+
+			// Now we know about this event, too.
+			known[event.EventID()] = types.Event{
+				EventNID: eventNID,
+				Event:    event,
+			}
 		}
 	}