In this article, we examine two word order inversion constructions in Mbuun, a Bantu language which lacks a true morphological or periphrastic passive. Mbuun uses both an OSV construction and an impersonal 3PL construction as functional passives. We demonstrate that the pre-posed object in both constructions is more than a mere topic in a syntactically adjoined position. It can be considered a syntactic argument and even displays certain properties which are generally associated with grammatical subjects. Hence, both constructions involve more than the pragmatic topicalization of the object. They are more than just functional passives. They have to some extent also evolved grammatically towards passiveness. Comparing the two Mbuun functional passives from a pragmatic point of view, the impersonal 3PL construction comes closest to passive prototype, because it obligatorily deletes the AGENT. In the related OSV construction, the AGENT is maintained in pre-verbal position, thus retains substantial topicality, and can even receive new information focus.