Wallace’s line is a biogeographical barrier to faunal movements between Southeast Asia and the Australo-Papuan region. There are exceptions among rodents and bats, few of which have crossed Wallace’s line. The gibbon ape leukemia viruses (GALV) and koala retrovirus (KoRV) have only been identified in wildlife on the Australo-Papuan side of Wallaces’s Line with the potential exception of partial sequences identified in two microbat fecal samples from China and a recently described GALV relative in a rodent from Africa. Here we describe a group of GALV-like endogenous retroviral sequences from the Southeast Asian flying lemur (Cynocephalus volans) representing the first known description of a primate relative which has been infected, and the germline colonized, by GALVs on the Southeast Asian side of Wallace’s Line.