This study analyzes the sociolinguistic distribution of /s/-aspiration, one of the realizations of syllable-final /s/ in Uruguayan border Spanish. It discusses aspiration as a new variant which is entering the dialect through the speech of the upper classes, in a process opposite to what has been reported by studies of (s) aspiration elsewhere. Because border Spanish is highly stigmatized and stereotypically a variety that maintains syllable-final (s) as full sibilants, aspiration enters the dialect as a prestige marker owing to its identification with the linguistic model of the speech of Montevideo. Data analysis reveals social and linguistic factors that condition the variable, and explores the role of aspiration as an ultra-local marker that has been incorporated by social groups who, by converging their speech with that of Montevideo, cause it to diverge from the local norm.