The article analyses the origin of two rubrics of Justinian’s Digest: De in diem addictionem (D. 18, 2) and De lege commissoria (D. 18, 3). A hypothesis on the creation of these rubrics and relative titles is envisaged: the Digest compilers would have decided (probably in the final phase of the sampling, in an attempt to bring the structure of the Digest into line with the material available to them) to disaggregate a ‘complex’ title D. 18, 1, already formed, extracting passages from it to form two new titles, which are the subject of the research.