We discovered a virus infecting Entomophthora muscae , a behavior-manipulating fungal pathogen of dipterans. The virus, which we name Entomophthovirus, is a capsid-forming, positive-strand RNA virus in the viral family iflaviridae, whose known members almost exclusively infect insects. We show that the virus RNA is expressed at high levels in fungal cells in vitro and during in vivo infections of Drosophila melanogaster , and that virus particles are present in E. muscae . Two close relatives of the virus had been previously described as insect viruses based on the presence of viral genomes in transcriptomes assembled from RNA extracted from wild dipterans. By analyzing sequencing data from these earlier reports, we show that both dipteran samples were co-infected with E. muscae . We also find the virus in RNA sequencing data from samples of two other species of dipterans, Musca domestica and Delia radicum , known to be infected with E. muscae . These data establish that Entomophthovirus is widely, and seemingly obligately, associated with E. muscae . As other members of the iflaviridae cause behavioral changes in insects, we speculate on the possibility that Entomophthovirus plays a role in E. muscae involved host manipulation.