This paper addresses the question whether listeners possess sociolinguistic knowledge of regional variation in a sound change affecting /s/ + voiceless stop sequences in Andalusian Spanish. We tested whether speakers from Seville and Granada were perceived as more Sevillian-sounding and as younger when a stimulus contained the novel phonetic variant, a post-aspirated stop. Word-medial syllable-final /s/ was manipulated in such a way that two stimuli of the same speaker differed only in whether they contained pre-aspiration ([eh.ˈtaŋ.ko]) or post-aspiration ([e.ˈthaŋ.ko]). Andalusian listeners rated the same speaker as younger and as more Sevillian-sounding when the stimulus contained a post-aspirated stop. The recognition of a speaker’s actual dialect was particularly high when the innovative variant was embedded in a Seville speaker’s speech, confirming earlier work that indexicality is context-specific. The results suggest that Andalusian listeners possess knowledge of the regional variation and the sound change and use this variation in social perception.