We show analytically that the two-dimensional Ewald summation of the Coulomb and dipole-dipole interaction energy may be approximated by the conventional three-dimensional Ewald method. However, an empty space must be introduced in the simulation box, and \M\(2)/3 must be replaced with M-z(2), where M is the total dipole moment of the system and M-z is its component along the nonperiodicity direction.