This paper presents an analysis of the mood/reality-status marking system of Djambarrpuyŋu (Yolŋu Matha: Pama-Nyungan), in particular as it relates to the phenomenon of "asymmetric negation" (in the sense of Miestamo 1995). On the basis of new data elicited in the field (Arnhem Land, northern Australia), it comprises the first formal treatment of the semantics of reality status in an Australian language, joining recent work on verbal mood in languages outside Europe. To this end, Phillips proposes a treatment of Djambarrpuyŋu verbal inflection as encoding a binary reality status distinction, where irrealis mood is modelled as comprising the presupposition that the conversational background is diverse with respect to the inflection's prejacent. This treatment aligns with theories that highlight the markedness of negative sentences vis-à-vis affirmative ones and, consequently, predicts patterns involving the neutralisation of reality status marking in negative contexts, as it is exhibited in Djambarrpuyŋu.