Constant-temperature constant-volume molecular dynamics simulations were performed for the fluoride-perovskite KCaF3. Ionic conductivity values were predicted using systems designed so as to simulate crystals containing extrinsic defects; these values were compared with experimental measurements made between 575 and 690 K. At these temperatures, extrinsic defects were found to be prerequisite for diffusion of fluorine ions. During defect-free simulations, intrinsic disorder was not generated spontaneously. Fluorine migration precedes via a discrete vacancy "hopping" mechanism, in which the anion migration time is of at least an order of magnitude less than the average residence time at a given lattice site. This is in contrast to the partially correlated mechanism observed at temperatures approaching the simulated melting point for KCaF3, in which vacancies are generated by the formation of fluorine ion pairs occupying interstitial sites.