diff --git a/roomserver/storage/postgres/state_snapshot_table.go b/roomserver/storage/postgres/state_snapshot_table.go
index 26ebcf856..99c76befe 100644
--- a/roomserver/storage/postgres/state_snapshot_table.go
+++ b/roomserver/storage/postgres/state_snapshot_table.go
@@ -77,21 +77,25 @@ const bulkSelectStateBlockNIDsSQL = "" +
 // helpers.CheckServerAllowedToSeeEvent function.
 // TODO: There's a sequence scan here because of the hash join strategy, which is
 // probably O(n) on state key entries, so there must be a way to avoid that somehow.
-const bulkSelectStateForHistoryVisibilitySQL = "" +
-	"SELECT event_nid FROM (" +
-	" SELECT event_nid, event_type_nid, event_state_key_nid FROM roomserver_events" +
-	" WHERE (event_type_nid = 5 OR event_type_nid = 7)" +
-	" AND event_nid = ANY(" +
-	"  SELECT UNNEST(event_nids) FROM roomserver_state_block" +
-	"  WHERE state_block_nid = ANY(" +
-	"   SELECT UNNEST(state_block_nids) FROM roomserver_state_snapshots" +
-	"   WHERE state_snapshot_nid = $1" +
-	"  )" +
-	" )" +
-	") AS roomserver_events" +
-	" INNER JOIN roomserver_event_state_keys" +
-	"  ON roomserver_events.event_state_key_nid = roomserver_event_state_keys.event_state_key_nid" +
-	"  AND (event_type_nid = 7 OR event_state_key LIKE '%:' || $2);"
+// Event type NIDs are:
+// - 5: m.room.member as per https://github.com/matrix-org/dendrite/blob/c7f7aec4d07d59120d37d5b16a900f6d608a75c4/roomserver/storage/postgres/event_types_table.go#L40
+// - 7: m.room.history_visibility as per https://github.com/matrix-org/dendrite/blob/c7f7aec4d07d59120d37d5b16a900f6d608a75c4/roomserver/storage/postgres/event_types_table.go#L42
+const bulkSelectStateForHistoryVisibilitySQL = `
+	SELECT event_nid FROM (
+	  SELECT event_nid, event_type_nid, event_state_key_nid FROM roomserver_events
+	  WHERE (event_type_nid = 5 OR event_type_nid = 7)
+	  AND event_nid = ANY(
+	    SELECT UNNEST(event_nids) FROM roomserver_state_block
+	    WHERE state_block_nid = ANY(
+	      SELECT UNNEST(state_block_nids) FROM roomserver_state_snapshots
+	      WHERE state_snapshot_nid = $1
+	    )
+	  )
+	) AS roomserver_events
+	INNER JOIN roomserver_event_state_keys
+	  ON roomserver_events.event_state_key_nid = roomserver_event_state_keys.event_state_key_nid
+	  AND (event_type_nid = 7 OR event_state_key LIKE '%:' || $2);
+`
 
 type stateSnapshotStatements struct {
 	insertStateStmt                         *sql.Stmt
@@ -170,15 +174,12 @@ func (s *stateSnapshotStatements) BulkSelectStateForHistoryVisibility(
 	}
 	defer rows.Close() // nolint: errcheck
 	results := make([]types.EventNID, 0, 16)
-	for i := 0; rows.Next(); i++ {
+	for rows.Next() {
 		var eventNID types.EventNID
 		if err = rows.Scan(&eventNID); err != nil {
 			return nil, err
 		}
 		results = append(results, eventNID)
 	}
-	if err = rows.Err(); err != nil {
-		return nil, err
-	}
-	return results, nil
+	return results, rows.Err()
 }
diff --git a/roomserver/storage/tables/interface.go b/roomserver/storage/tables/interface.go
index cf64ca28a..58c43ac45 100644
--- a/roomserver/storage/tables/interface.go
+++ b/roomserver/storage/tables/interface.go
@@ -83,6 +83,9 @@ type Rooms interface {
 type StateSnapshot interface {
 	InsertState(ctx context.Context, txn *sql.Tx, roomNID types.RoomNID, stateBlockNIDs types.StateBlockNIDs) (stateNID types.StateSnapshotNID, err error)
 	BulkSelectStateBlockNIDs(ctx context.Context, txn *sql.Tx, stateNIDs []types.StateSnapshotNID) ([]types.StateBlockNIDList, error)
+	// BulkSelectStateForHistoryVisibility is a PostgreSQL-only optimisation for finding
+	// which users are in a room faster than having to load the entire room state. In the
+	// case of SQLite, this will return tables.OptimisationNotSupportedError.
 	BulkSelectStateForHistoryVisibility(ctx context.Context, txn *sql.Tx, stateSnapshotNID types.StateSnapshotNID, domain string) ([]types.EventNID, error)
 }