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Krasinsky and Brumberg (2004 Celest. Mech. Dyn. Astron., 90, 267) reported a secular increase of the astronomical unit (AU) of 15 meters per century. Recently, Miura et al. (2009, PASJ, 61) proposed that a possible angular momentum transfer from the rotation of the Sun to the orbital motion of the solar system planets may explain the observed increase of the AU. They assumed that the tidal effect between the planets and the Sun is the cause of this transfer. Here we claim that tidal effect cannot be a cause of this type of the transfer to explain the increase of the AU., Comment: 3 pages, no figures. Accepted for publication in Publications of the Astronomical Society of Japan