In light of speculation in the recent literature concerning the species' intraspecific taxonomy and personal observations, we examined specimens of the Mascarene Swiftlet Aerodramus francicus from both range islands, Mauritius and Reunion, with the aim of documenting any geographical variation in morphology. We found that specimens from Reunion clearly differ from those collected on Mauritius (the type locality) in multiple plumage and biometric characters, and that at least some of these differences are also visible in the field. As a result, we describe the Reunion population as a new subspecies under the Biological Species Concept. Taken together, these insular forms are treated by BirdLife International as Near Threatened, but the declining nominotypical Mauritian population might require a reassessment of its conservation status according to IUCN criteria should future taxonomic research applying an integrative approach indicate that species rank is more appropriate.