This paper examines the interference of L1 neutralization rules in the acquisition of a markedL2 phonological feature. More specifically, it presents results from a study of the acquisition ofthe voicing contrast in English word-final obstruents by native speakers of Catalan. The voicingcontrast in final position in Catalan is neutralized by voicing or devoicing rules, depending onthe environment. The results of an experiment testing the production of target final obstruents indifferent environments indicate a very high incidence of devoicing, which confirms theprevalence of final devoicing in second language acquisition and points to the joint effect oftransfer and universal tendencies. In contrast with devoicing, the results reveal a more limitedeffect of the L1 voicing rules. It is argued that this difference is due to an effect of word integrityin the interlanguage that restricts the domain of application of the transferred rules.