This article documents and analyzes a system of suppletive alternations that are conditioned by top-down prosodic context. In Mandar (Austronesian), seven heads supplete at the right edge of the phonological phrase to satisfy an output constraint on foot structure. When phraseexternal phonological context makes it possible to resolve this output constraint in a more optimal way, these patterns of suppletion are suspended. These effects suggest that the mechanism that regulates suppletion, Vocabulary Insertion, must be situated within a phonological calculus that can access global context and respond to output constraints.