According to the jurisprudence of the Federal Constitutional Court – recently confirmed in the Treaty Override decision of December 2015 – the executive has the competence to terminate international treaties without parliamentary approval. In contrast, the British Supreme Court and a South African High Court decided in February/March 2017 that parliamentary participation in the termination of the Treaty on European Union and in the withdrawal from the Rome Statute of the International Criminal Court are required by the respective constitutional laws. Against the background of the two judgments, this article critically assesses the case law of the Federal Constitutional Court. The author starts from the premise that foreign decisions can only have an impact on German constitutional law doctrine if the respective constitutional arguments fit into the German context. On this basis, the decision of the British court provides no guidance for German constitutional law, as it is too closely intertwined with the specific circumstances of Brexit. However, the actus contrarius concept – the argumentative bedrock of the South African judgment – compels us to rethink the existing case law of the Federal Constitutional Court. Moreover, the parlamentarization of foreign affairs in German constitutional law doctrine suggests that a proper interpretation of Art. 59 Basic Law should involve Parliament in the decision to terminate international agreements.