The acoustic radiation self-impedance and mutual impedances for rectangular pistons on a rigid corner of any angle are derived and compared with approximate expressions. The resistances are obtained from the pressure in the far field, and the reactances are related to the resistances by the use of the Kramers-Kronig (or dispersion) relations. Numerical results are presented. It is shown that the self-impedance is almost independent of the corner angle when the piston is at a distance of a wavelength or more from the edge of the corner, while the mutual impedance is affected relatively more.