The paper deals with recent deviations from the shared values of constitutionalism towards a kind of ‘populist, illiberal constitutionalism’, particularly in East-Central Europe. The theoretical question that these backslidings raise is whether populism and illiberalism are reconcilable with constitutionalism at all. The paper concentrates on a particular version of populism, which is nationalist and illiberal, and mainly present in the countries of East-Central Europe. Most are also members of the European Union, a value community based on liberal democratic constitutionalism. The paper concludes that the term ‘populist constitutionalism’ is an oxymoron altogether, consequently, it equates constitutionalism with liberal democratic constitutionalism. This does not mean, however, that constitutions cannot be illiberal or authoritarian. But in illiberal polities, just like in the East-Central European ones, there is no constitutionalism.