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