Many cosmic dust species, among them refractory oxides, form at temperatures higher than 300K. Nevertheless, most astrophysical studies are based on the room-temperature optical constants of solids, such as corundum and spinel. A more realistic approach is needed for these materials, especially in the context of modeling late-type stars. We aimed at deriving sets of optical constants of selected, astrophysically relevant oxide dust species with high melting points. A high-temperature, high-pressure cell and a Fourier-transform spectrometer were used to measure reflectance spectra of polished samples. For corundum ({alpha}-Al_2_O_3_), spinel (MgAl_2_O_4_), and {alpha}-quartz (SiO_2_), temperature-dependent optical constants were measured from 300K up to more than 900K. Small particle spectra were also calculated from these data.