This paper deals with a famous passage by Theopompus concerning the hetairoi of Philip II. Athenaeus, one of the three authors who transmitted this fragment to us, states that Philip had 800 hetairoi in 339, which seems to be too low a number for the last years of the reign. In search of a solution which would match Athenaeus’ quotation from Theopompus with other data about Macedonian cavalry under Philip and Alexander, I consider a textual corruption in Athenaeus.