Comment: 14 pages, 3 figures, 7 tablesSwiss-system is an increasingly popular tournament format as it provides an attractive trade-off between the number of matches and ranking accuracy. However, few empirical research consider the optimal design of the Swiss-system. We contribute to this issue by investigating the fairness of Swiss-system chess competitions with an odd number of rounds, where half of the players have an extra game with white pieces. They are proven to enjoy a significant advantage and to be overrepresented among both the highest-ranked and outperforming players. Therefore, Swiss-system tournaments should have an even number of rounds and use a pairing mechanism that guarantees a balanced colour assignment.