This paper investigates the morphosyntax of unaccusative structures in Me'phaa (ISO 639-3: tcf) and their implications for the syntax of root suppletion. Bobaljik & Harley (2017) develop an account of Hiaki number-conditioned verb suppletion that is (a) independent of agreement mechanisms and (b) relies on stringent locality constraints, such that the trigger for suppletion must be sister to the verb root. In contrast to this, I show that for Me'phaa, person/number-based verbal suppletion is part of the overall agreement paradigm, and that internal arguments sister to the verb root never trigger suppletion. Instead, the internal arguments that trigger suppletion are situated in an unaccusative structure where they are more deeply embedded in a small clause complement structure (Irwin 2012, 2016). Me'phaa thus furnishes evidence that agreement mechanisms can indeed feed verb suppletion – an "unresolved issue" for Bobaljik & Harley (2017: 158). Me'phaa facts also reveal the need to refine Bobaljik & Harley's definition of locality so that internal arguments not sister to the verb root can serve as the trigger of suppletion.