Tswana is traditionally described as having a process of post-nasal devoicing (/mba/ > [mpa]). If this is accurate, then Tswana poses a challenge to views that neutralization processes should be articulatorily grounded. Airflow leakage through the nasal cavity should promote, not inhibit, voicing post-nasally. Zsiga et al. performed acoustic analysis of the speech of 6 Tswana speakers, and found no evidence of post-nasal devoicing. They conclude that, counter to traditional descriptions, Tswana does not have post-nasal devoicing. In an independent study, we collected speech from 12 Tswana speakers. Four of our speakers showed clear and consistent post-nasal devoicing. In this paper, we present the data for these 4 speakers to show that at least some speakers of Tswana do have an active process of post-nasal devoicing. We also consider possible explanations for this process, arguing that it is motivated by perceptual rather than articulatory considerations.