In November 2019, KU Leuven acquired a unique early printed book, viz. the personal copy of a Hippocrates edition (Basel: Johann Bebel & Michael Isengrin, 1537) once owned by Petrus Nannius (Nanninck; 1496–1557), best known as the third Professor of Latin at the Leuven Collegium Trilingue. This acquisition is first and foremost interesting from a bookhistorical point of view. On the one hand, the book gives us an insight into the library of one of the most important Latinists of the Southern Low Countries during the first half of the sixteenth century, on the other hand it provides us with new information on the earliest known (and accurately datable) auction of a private book collection in Leuven. First, this article delves deeper into the history of ownership of this recent acquisition, with special attention being paid to the different provenance notes, other signs of usage, and in particular, the auction organised in the wake of Nannius’ death (†21 June 1557). In the second part of this contribution I offer an onset to a further reconstruction of Nannius’ personal library.