The recently erected phyllophorid genus Massinium Samyn & Thandar, 2003 hithertho held three species: the southern African endemics Massinium arthroprocessum (Thandar, 1989) and M. maculosum Samyn & Thandar, 2003 (type species), and the central Indo-Pacific M. magnum (Ludwig, 1882). Careful examination of the incomplete holotype of M. magnum and material assigned to this species from various museums allowed us to completely redescribe the type, supplement the description with information from entire voucher specimens, and recognise two species new to science, previously assigned to M. magnum. In addition, the diagnosis of Massinium is amended to also include Neothyonidium dissimilis Cherbonnier, 1988 from Madagascar. The six currently recognised congenerics are keyed.