In an interlocutory decision rendered on 16 February 2011 the Appeals Chamber of the Special Tribunal for Lebanon held that terrorism has evolved into a crime under international customary law. The following comment will show that the decision is based on two major errors: First, it can be shown that for the tasks at hand it was absolutely unnecessary for the Appeals Chamber to resort to any endeavour to establish whether terrorism was a criminal offence under international customary law or not (III.). Second, the finding that a customary rule of international law regarding the international crime of terrorism had emerged is based on insufficient grounds and cannot be upheld (IV.). Rather than triggering speculation as to what caused the judges to be led astray to such a significant extent, the decision will hopefully serve to stimulate a discussion that is long overdue and goes to the heart of international criminal law, namely the legitimacy and reach of customary international criminal law (V.).