A retardation correction to the high-energy limit of the dipole photoionization cross section and to the ratio of the double-to-single electron photoionization cross sections is calculated. This correction comes from the quasifree mechanism of the two-electron photoionization and is determined by the probability to find both ionizing electrons at the same point in the initial state. The calculations are performed for ${\mathrm{H}}^{\ensuremath{-}},$ the helium atom and the heliumlike ions in the ground and some excited states using high-precision wave functions. The nuclear charge dependence of this correction for heliumlike ions in the ground and four lowest ${}^{1}S$ exited states is calculated. The possibility to detect this correction experimentally is discussed.