This paper investigates the morphosyntax of number and gender agreement in English-dominant heritage speakers of Spanish. Our study builds on the experimental paradigm of agreement attraction developed by Fuchs et al. (2015) and elicits responses to agreement failures to diagnose the potentially-independent contributions of number and gender features. By comparing the structuring of these agreement categories in native and heritage Spanish, we document a case of grammatical divergence: heritage speakers restructure their agreement categories, favoring fewer feature values and less structure. The principled nature of this restructuring demonstrates that the loss of agreement in heritage languages is not superficial or accidental, but rather follows from predictable structural changes.