In this article I am interested in seeing what the normative jurisprudential support is for a minimalist version of habeas corpus in international law. I investigate what Fuller called'procedural natural law' in contemporary international criminal law. In the first two sections I rehearse some of Hart's and Fuller's views as they pertain to the subject of international law and also to the inner morality of law. In the third section I set out some of my views on these matters, drawing on both Hart and Fuller, concerning the value of fundamental procedural rights. In the fourth section I discuss the right of habeas corpus as a good test case of how to think about these issues. In the final sections I expand on these remarks and argue that procedural rights need to be protected better in international law, if the latter is to have a claim to legitimacy as amature legal system.