Abstract In the history of various European languages (Latin, Spanish, English, Swedish, and various dialects of French) there are instances of the cluster mn appearing as mpn. There are philological controversies as to whether this ‘epenthetic’ p was actually pronounced or was just a learned hypercorrect spelling. I offer here a novel phonetic scenario supporting the claim that the p was pronounced and arose in a phonetically natural way: I posit that in the mn cluster there was temporal overlap of the m and n closures. The simultaneous labial and apical closure would create a pocket of air between them which, when the labial closure was released, would undergo a momentary rarefaction of pressure and thus be released with a click-like burst. Listeners would be likely to interpret this stop burst auditorily as a pulmonic [p] and this would be the basis of their own pronunciations.