This paper examines the interference of L1 neutralization rules in the acquisition of a marked L2 phonological feature. More specifically, it presents results from a study of the acquisition of the voicing contrast in English word-final obstruents by native speakers of Catalan. The voicing contrast in final position in Catalan is neutralized by voicing or devoicing rules, depending on the environment. The results of an experiment testing the production of target final obstruents in different environments indicate a very high incidence of devoicing, which confirms the prevalence of final devoicing in second language acquisition and points to the joint effect of transfer and universal tendencies. In contrast with devoicing, the results reveal a more limited effect of the L1 voicing rules. It is argued that this difference is due to an effect of word integrity in the interlanguage that restricts the domain of application of the transferred rules.