A contentious issue in the Minimalist literature is whether certain phenomena are best described in terms of features or constraints. Building on recent work in mathematical linguistics, I argue that constraints and features are interchangeable in Minimalist syntax. This does not invalidate the feature-constraint debate, though. Rather, the interdefinability of the two points out an unexpected loophole in the formalism that allows for massive overgeneration and produces incorrect typological predictions. At the same time, the feature-constraint equivalence can be helpful in plugging this loophole.