This paper discusses the simplification of forms ending in obstruents by native speakers ofMandarin, in particular two effects that are not obviously motivated by either the native- or thetarget-language grammars: a tendency to devoice final voiced obstruents and a tendency tomaximize the number of bisyllabic forms in the output. These patterns are accounted for withinOptimality Theory, which describes a grammar as a set of universal, ranked constraints. It isargued that the devoicing and bisyllabicity effects result from universal markedness constraintsthat are present in all grammars but that are masked in the learner's native-languagegrammar by the effects of higher ranking constraints.