This article discusses the origin and historical development of the German n-indefinite kein , which is an unusual negator because it does not share the initial n that marks virtually all other negatives in German. Despite the discussion about its origins going back to the nineteenth century, it is still unclear how kein first emerged and out of which other forms it developed. In this paper, new light is shed on an old controversy using new data and modern corpus-linguistic tools, in this case the Referenzkorpus Mittelhochdeutsch (ReM). The article first summarises the current state of research before presenting and analysing the data. In combination with additional evidence, the results show that certain hypotheses that have to this day been treated as accurate are in fact not viable. Subsequently, a solution that combines some of the existing theses and is compatible with the data is presented: Morphological reanalysis and the ensuing back-formation of kein’ s predecessor nehein – in combination with a phonologically conditioned sound substitution triggered by a shift of the syllable boundary – in the context of negative concord seems the most likely candidate for an accurate explanation of the emergence and early usage patterns of kein in Middle High German. Incongruent evidence from Swiss German, however, suggests that partially convergent developments ensuing from different indefinite forms have taken place in that variety.