A genetic subgrouping of 16 East Chadic languages is proposed in this paper. Contrary to the popular lexicostatistical approach, and in order to take into account potentially different rates of lexical evolution in the individual languages, it is attempted here to rely on the identification of common innovations. A practical method is presented how to apply the notion of common innovation when working with lexical isoglosses. This new method can also serve as a model for the subgrouping of language families other than East Chadic.