Absence of a discrete, externally visible gender-specific character makes sex determination of the rubber plantation litter beetle, Luprops tristis Fabricius (Coleoptera: Tenebrionidae: Lupropini), a difficult task. A new method based on a distinct notch on the 8^th sternite of males that can be used to distinguish the sexes is described. This is the only method by which accurate sex determination of L. tristis could be done when culturing of live specimens is required. All alternative methods were found to be either inaccurate or led to higher mortality.