In this paper we show that the Bantu A70 languages did not preserve the passive morpheme inherited from Proto-Bantu (PB), but developed a new suffix. It is a morpheme that is compound in origin, consisting of two verbal derivation suffixes which still function independently in today s languages as a middle marker and an associative/reciprocal marker respectively, though with variable degrees of productivity. The genesis of a passive marker from the stacking of two pre-existing suffixes is a typologically rare evolution path, but it fits in with a wider Bantu phenomenon of double verb extensions which develop non-compositional meanings. Especially double extensions involving the Proto- Bantu associative/reciprocal marker *‑an- tend to develop such idiosyncratic meanings. This suffix is also one of the constituents of the Bantu A70 passive marker. Nevertheless, even within Bantu, the emergence of a productive passive marker from such double extension is unique. In this paper, we argue that the notion of co-participation may account for the rising of this passive meaning out of the stacking of the common Bantu associative/reciprocal suffix to a common Bantu middle suffix. The semantic development of this compound suffix (and its historical constituents) happened within the semantic continuum that links reciprocals, reflexives, middles and passives in many languages of the world, but did not necessarily follow the typologically common reflexive > reciprocal > middle > passive cline.