Despite being an embarrassing and rarely-addressed issue in the early Church, sexual dreams were ardently discoursed by Augustine and Cassian. In their discussions, not only sexual dreams became an indicator of the dreamer’s moral disposition but a moral hierarchy of dreamers was created for the first time in Christianity. Moreover, while many early and modern Christians consider dreaming of concupiscent images or having a nocturnal emission as sinful, surprisingly these two church fathers doctrinally justified oneiric sexual sinners as innocent. Their doctrine of sin converted the dominion of dreams into the only place where people were inculpable for their ‘sinful deeds’. This article examines their conception of sexual dreams and their articulation of the doctrine of sin by them.