It is shown that the recently published work of Pandey and Dwivedi [J. Plasma Phys. 55, 395 (1996)] dealing with dust-acoustic waves in a self-gravitating unmagnetized dusty plasma is erroneous. This is demonstrated on the basis of a dispersion relation in which gravitational and electrostatic forces are kept on an equal footing. Furthermore, a general linear dispersion relation for the dust-acoustic and dust-ion acoustic waves in self-gravitating dusty plasmas is obtained, taking into account the dust-charge perturbations. Specific results for limiting cases are discussed.