We report the results of a high-resolution differential thermal analysis (DTA) performed on the solid electrolyte RbAg4I5 through the order-disorder transition at T-c = 209 K. The experiments were carried out on pure single-crystal specimens, in which AgI was used as reference sample. The DTA results show a small latent heat at T-c that provide evidence for a "weakly first-order transition" as previously proposed.