This paper discusses passivization in Vedic Sanskrit and Ancient Greek, two ancient Indo-European languages. These languages have two different types of synthetic passive: the inflectional passive, which expresses passivization by selecting a specific set of nonactive (“middle”) endings, and the derivational passive, which uses a specifically passive suffix, to which inflectional endings expressing Tense, Aspect, and Voice are then added. While the inflectional passive in both languages can be analyzed along the lines proposed by Alexiadou et al. 2015 for Modern Greek passives, the main focus of this paper is on the derivational passives and their apparent “double marking” of Voice (via a designated suffix and via the inflectional endings). I argue that the suffix of the derivational passive is a diachronically reanalyzed inchoative v head that turned into a “low” passive head, providing further evidence for the cross-linguistic parametrization of passive morphosyntax.