Within the genus Cacosternum, the species C. capense and C. namaquense form a clade defined by their robust morphology, large size, and distinct dorsolateral glands. In this study, we describe a third member of the group endemic to the Cederberg region of South Africa. Specimens from this area have historically been assigned to C. karooicum, but here we show that this population is genetically unrelated. Using a combination of molecular, morphological, and acoustic data, we provide evidence to show that the Cederberg population of C. karooicum represents an undescribed species within the C. capense group. The new species can be diagnosed from its closest phylogenetic relatives, C. capense and C. namaquense, by the absence of a dark streak running downwards from the pupil into the iris, the presence of large rictal glands that form an uninterrupted arc with the angle of the jaw, heart-shaped palmar tubercles, and an advertisement call with a dominant frequency below 2 kHz. We further discuss their natural history, distribution, and conservation.