In the article, the author examines the modern term "fundamental violations of the law". The author analyzes the decisions of the European Court of Human Rights and the Constitutional Court of the Russian Federation in the question of establishing special grounds for a turn for the worse after the sentence comes into force. Particularly, it is noted that the European Court of Human Rights takes the position that it is impossible to reverse a sentence and turn to the worse, if such a reversal is caused by mistakes made by a court or by investigative bodies. On the other hand, the Constitutional Court of the Russian Federation affirms that the impossibility of a reversal of a sentence in force violates the constitutional rights of the victim. Furthermore, the article analyzes specific scientific literature and cassation practice of courts which witness the absence of the criteria for the definition of violations of the law as fundamental. It is noted that such a situation in law enforcement negatively affects the legal status of a convict and leads to legal uncertainty in the question of a reversal of a sentence that is in force. This situation may be overcome in different ways, in particular: 1) the removal of all restrictions of a turn for the worse a year after a sentence has come into force; 2) the prohibition of a turn for the worse after the sentence has come into force, regardless of the produced violations of the law; 3) the possibility of a reversal of a sentence in force on the general cassation grounds, but only on the basis of an appeal of a victim. The analysis of the pros and cons of all options to solve this problem leads to a conclusion that in modern Criminal Procedure Code of the Russian Federation it is necessary to abandon the practice of picking out "fundamental violations of the law" and allow a repeal of a sentence in force on the general cassation grounds. Legal stability must be achieved by limiting the parties who may appeal against a sentence, and not by special grounds for a turn for the worse. This solution will allow taking into account the legal position of the Constitutional Court of the Russian Federation and the European Court of Human Rights, and providing a proper balance between the constitutional interests of a convict and a victim.