Like other languages of the Sotho-Tswana subgroup of Bantu, Shekgalagari exhibits a process of post-nasal devoicing, a phenomenon which has been at the center of the debate on the phonetic grounding of phonology. The existence of post-nasal devoicing has been questioned, and it has been claimed that it is phonetically unnatural. In this paper, we provide instrumental data that post-nasal devoicing actually exists in Shekgalagari and suggest that it is not necessarily phonetically unnatural. Acoustic and laryngographic data indicate that post-nasal devoicing is a categorical process, i.e., devoiced stops do not differ from underlying voiceless stops in any of the durational, voicing and tonal parameters analyzed. Voiced stops differ from devoiced and voiceless stops in all these parameters. Secondly, the results show that in Shekgalagari (as in Tswana) voiceless stops do not have longer voicing into the closure postnasally than postvocally, in contrast with the findings for most languages. These results undercut the claim that the tendency towards postnasal obstruent voicing is present in all languages. We argue that the two patterns, postnasal voicing and devoicing, may not be as antagonistic as has been assumed, and that both may be derived from a common source, variations in the relative timing of the nasal and oral gestures.