The doctrine of “unconstitutional constitutional amendments” has obtained a growing acceptance by distinct constitutional courts across the world and been largely studied in comparative constitutional law. The constitutional literature has basically concentrated on the courts’ behavior and their decision-making. But what about parliaments? Sometimes depicted as the villains in cases of potential violation of an explicit or implicit constitutional amendment, they may nonetheless behave as an important first shield against such proposals for constitutional amendments, even if not successful in the end. Drawing from the Latin American experience and theories of political behavior, this paper adresses the role of parliamentary oversight organs and their internal political debates and decisions as another fundamental, though overlooked, institution in the protection of constitution.