In standard Basque and in most present-day dialects, coding frames that were exceptional in Old Basque are attested by a sizeble proportion of the verbal lexicon, which results in a system characterized by a typologinally uncommon type of split intransitivity. In this paper, we discuss the factors that may have payed a role in the expansion of ergative encoding and more specifically of the coding frames and , which originally were clearly non-canonical. We argue that the situation observed in present-day Basque implies a change in the constraints underlying the organization of the valency properties of Basque verbs or in their relative ranking.