The paper deals with the process of reforming in peius, which marks one of the important means for the fairness of the right to a fair trial. It gradually analyzes its regulation in the Code of Administrative Procedure, the Act on Liability for Offenses, the Tax Code and the disciplinary law, and draws attention to the problematic aspects of the legal regulation. It implies that the crucial role in practice is whether or not the wider or narrower concept will be applied.