As one of the last books he produced, John Mair published in 1530 a huge commentary on Aristotle's Nicomachean Ethics. Concerned with the challenges of his time – the intra-scholastic quarrels, the humanist critique of scholasticism, and the Reformation – he dove into the writing of his commentary. He hoped to be able to reassure the traditional world view and approaches while arguing for an almost perfect concordance of Aristotle, the champion of natural reason, and the traditional catholic faith. In doing so, an important resource to test Aristotle's orthodoxy was Augustine, such that the commentary became an interesting conglomerate of philosophical and patristic sources. This paper analyzes the presence of Augustine in the context of philosophical ethics, arguing that references to the Church Father were used quite flexibly, adapted to the goals of the commentary and going as far as to conceal the Augustinian authority of certain passages in order to show the conformity of Aristotle with Christian doctrine. Given the far-reaching presence of Augustine (and other Church Fathers) in this philosophical commentary, this paper also argues for the possible transmission of theological knowledge to Mair's students of philosophy, which may have included John Calvin.