A solid-state laser cavity is studied where the laser crystal aberrations are corrected by a diffractive optic element. The type of aberration and the location of the correction plate are found to significantly influence the modal performance of the cavity. The largest modal discrimination is obtained for axicon-like crystal aberrations and when the correction is performed close to the end mirror. An experiment is performed with a laser-diode-pumped Nd:YVO4 laser. With no correction, a thermal aberration of approximately two waves is measured across the crystal. By using a diffractive corrector plate, the single-mode slope efficiency is increased by a factor of 4, and the total single-mode output power is increased by a factor of 3.