In this paper, I will argue that the Slovak constitutional system consists not only of the written sources of law but also of constitutional conventions understood as a specific legal custom. Most Slovak constitutional lawyers believe that this kind of unwritten legal rule regulates the process of forming a new government after the announcement of the parliamentary election results. Namely, according to the generally shared constitutional convention, the President is obliged to entrust the assignment to form a new government to the representative of a political party with the highest number of votes obtained. I subsequently explore whether it is tenable given the conditions of the Slovak Republic to enforce such conventions by the judiciary. The analysis of the relevant case-law shows that the Slovak Constitutional Court refers to constitutional conventions in its legal argumentation only rarely. And even when it does, usually it is not particularly convincing. Especially, the Court’s reasoning by constitutional conventions related to the President’s appointing powers is loaded with misconceptions and contradictions, so one could wonder whether constitutional conventions serve only as a façade for the Court’s arbitrariness. Despite this harsh assessment, I conclude that there are good institutional reasons for entrusting the Constitutional Court with enforcing constitutional conventions, including particularly the one regulating the assignment to form a new government.