The angular size of a star is a critical factor in determining its basic properties. Together with the distance, it provides the physical diameter of the star which can be used to yield luminosity and mass estimates. Direct measurement of stellar angular diameters is difficult: at interstellar distances stars are generally too small to resolve by any individual imaging telescope. This fundamental limitation can be overcome by several methods using Imaging Atmospheric Cherenkov Telescopes: By studying the diffraction pattern in the shadow cast when an asteroid occults a star, or by performing intensity interferometry observations. Atmospheric Cherenkov telescopes used for particle astrophysics observations have not generally been exploited for direct optical measurements due to the modest optical quality of their mirror surface. However, their optical design and large mirror area makes them well suited for such high-time-resolution measurements. Here we report on recent measurements using the VERITAS telescopes, and discuss about the future of sub-mas astronomy with IACTs.