Two proposed modifications to the standard theory for the long-wavelength absorption by interstellar dust grains are shown to be incorrect. The Mie theory for spheres or cylinders, or the discrete dipole approximation for irregular shapes, are based on Maxwell's equations for the electromagnetic field and should be used instead of the modified formula proposed by Duley et al. (1989). The calculated absorption cross sections should not be corrected for stimulated emission, since enhanced absorption from excited states exactly cancels the negative absorptions from stimulated emission. 11 refs.