Pre-stopping is a widespread and usually non-contrastive phenomenon in Australian languages. Contrastive pre-stopping is rare and materials on it are limited. Based partly on original phonetic data, this paper provides evidence that Arabana, a language of northern South Australia, has contrastive pre-stopping of both laterals and nasals. Current analyses of pre-stopping, both contrastive and non-contrastive, model pre-stopped sequences as complex segments, and relate their diachrony to perceptual motivations favouring the enhancement in the discrimination of place oppositions. We provide evidence that pre-stopped sequences in Arabana are best analyzed as heterosyllabic clusters, and that their diachrony centrally involves perceptual motivations favouring the augmentation of phonologically strong constituents, specifically stressed syllables.