Descartes argues that the mind and body are really distinct substances. He also insists that minds and bodies compose human beings. But how are mind and body united to compose a human? This question is crucial to understanding the place of human beings in Descartes's ontology. Many scholars argue that Descartes has no solution to the unity problem, and they call into question the ontological status of mind-body composites. On some views, Cartesian humans are mere aggregates, like stacks of pancakes; on other views, Descartes is not entitled to the view that humans exist at all. I argue that Descartes has a solution to the unity problem, and that he appropriates this solution from contemporaneous Jesuit discussions of soul-body unity-discussions that remain mostly unknown to contemporary scholars. The upshot is that Descartes has the metaphysical machinery to account for mind-body unity and doesn't have to say that a human being is like a stack of pancakes.