Sugars are an important class of nutrients found in the flowers and fruits of flowering plants. Although T1R2-T1R3 has been identified as the mammalian sweet receptor, some birds rely on a repurposed T1R1-T1R3 savory receptor to sense sugars. Moreover, as the radiation of flowering plants occurred later than the last common ancestor of amniotes, sugar may not have been an important diet item for amniotes early in evolution, raising the question of whether T1R2-T1R3 is a universal sugar sensor or only a mammalian innovation. We examined the molecular basis of sugar detection in a lizard, a representative of an understudied but phylogenetically relevant group of amniotes. Using brief-access behavioral tests and functional characterization of taste receptors, we demonstrated that the nectar-taking Madagascar giant day geckos (Phelsuma grandis) significantly preferred sugar solutions (sucrose, fructose and glucose) over water and can detect sugars using the canonical mammalian sweet receptor T1R2-T1R3. These results revealed the existence of T1R2-mediated sweet taste in a non-avian reptile, which has important implications for our understanding of the evolutionary history of sugar detection in amniotes.