Listeners in fixed-stress languages are less sensitive in processing stress contrasts in a second language with contrastive stress (stress 'deafness'). We investigated whether native speakers of French (fixed-stress language) can acquire the ability to distinguish stress contrasts in Spanish (free-stress language). In behavioral experiments, we found that French listeners were able to improve their ability to discriminate stress contrasts in Spanish after a 4-h training. This indicates that French listeners' stress detection disadvantage can be reduced by a short exposure to L2 stress contrasts. An ERP experiment administered after the training evidenced that the larger the P3b amplitude, the better the listeners' training outcome. In contrast, listeners' performance was not reflected by the N2b amplitude. In other words, listeners with high performance after training showed similar auditory sensitivity to stress in comparison to listeners with poor performance, but they better maintained stress information in working memory, as indicated by the larger amplitude of P3b. The present research indicates that individual differences in working memory processing should be considered in the acquisition of second language prosody.