In many jurisdictions, doctrines of unjust enrichment tend to be hotly contested. Not infrequently authors have turned to the Roman law as model system and template for the rational organization of contemporary laws. The legal historian must push back against the weaponization of Roman law. Approached soberly, the elements of Roman law which offer themselves for categorization as ‘unjust enrichment’ do not come across as a system of unjust enrichment, designed from first principles. The ‘change of position’-defense, a signature feature of unjust enrichment, will be the leitmotif of the paper.