diff --git a/roomserver/storage/shared/storage.go b/roomserver/storage/shared/storage.go
index 7e07096a8..e270e121c 100644
--- a/roomserver/storage/shared/storage.go
+++ b/roomserver/storage/shared/storage.go
@@ -13,6 +13,7 @@ import (
 	"github.com/matrix-org/dendrite/roomserver/types"
 	"github.com/matrix-org/gomatrixserverlib"
 	"github.com/matrix-org/util"
+	"github.com/sirupsen/logrus"
 	"github.com/tidwall/gjson"
 )
 
@@ -1100,6 +1101,9 @@ func (d *Database) JoinedUsersSetInRooms(ctx context.Context, roomIDs []string)
 	if err != nil {
 		return nil, err
 	}
+	if len(nidToUserID) != len(userNIDToCount) {
+		logrus.Warnf("SelectJoinedUsersSetForRooms found %d users but BulkSelectEventStateKey only returned state key NIDs for %d of them", len(userNIDToCount), len(nidToUserID))
+	}
 	result := make(map[string]int, len(userNIDToCount))
 	for nid, count := range userNIDToCount {
 		result[nidToUserID[nid]] = count