Borneo has been described by Blust as a “hot spot” for linguistic change. The densely forested highlands and river systems are home to numerous communities, and a long history of human occupation has created a complex network of languages and dialects. Recently, Borneo has been the focus of numerous comparative works, many dealing with the Kenyah, Kayanic, Penan, and Sebop language groups of Sarawak and East Kalimantan. This paper addresses the Kayan-Kenyah hypothesis of Antonia Soriente. By carefully considering the linguistic evidence, it is shown that Soriente’s hypothesis does not provide a convincing argument for a Kayan-Kenyah subgroup. Rather, there is a significant body of evidence for assuming that Kenyah, Penan, and Sebop form a single subgroup that does not include Kayanic. Furthermore, Soriente’s Kayan-Kenyah hypothesis includes an internal subgrouping that places many demonstrably Kenyah languages within the Kayanic subgroup. This paper also addresses these issues, and proposes an updated internal subgrouping based largely on the regular and highly distinctive split in Proto-Austronesian voiced stops shared by all Kenyah, Penan, and Sebop languages.