This paper investigates the ascription of a passage in Isidore’s Differentiae to the jurist Modestinus. A collection of philological notes by the humanist scholar Barthius reports the existence of a (now lost) manuscript that credited lemma 1.434 Codoñer to one Orenius, which has ever since usually been emended into Herennius (sc. Modestinus). It is possible to place this witness in the stemma of the Differentiae. Careful study of Barthius’ reported readings from the manuscript not only indicates that it was peripheral (...) to the tradition, but it also allows us to point out the (skilful) hand of an editor/interpolator, who may have been responsible for the addition of the name Orenius. (shrink)