This paper examines plural suppletion in the Barguzin dialect of Buryat (Mongolic, Russia), which occurs only in accusative and genitive noun phrases. The restricted distribution of this process, specifically its absence in oblique cases, is significant for recent research on the typology of suppletion and the feature structure of case. For much work in this vein, this plural suppletion would qualify as having an ‘ABA’ pattern, which is predicted to be unattested. I argue that the suppletive plural morpheme in question is a portmanteau whose morphological requirements cause it to conflict, for independent reasons, with the realization of oblique noun phrases. Consequently, I argue that its distribution does not falsify the theories that normally ban ABA patterns, but rather instantiates a principled exception to them which sharpens our understanding of them.