  We comment on the calculation mistake in the paper "w and w' of scalar field
models of dark energy" by Takeshi Chiba [arXiv:astro-ph/0510598], where w is
the dark energy equation of state and w' is the time derivative of w in units
of the Hubble time. The author made a mistake while rewriting the phantom
equation of motion, which led to an incorrect generic bound for the phantom
model and an incorrect bound for the tracker phantom model on the w-w' plane.
