  In a recent letter Marciano and Sirlin (Phys. Rev. Lett. 96, 032002, (2006))
presented an improved calculation of the electroweak radiative correction to
derive a precision value of the quark mixing angle $V_{ud}$ by improving the
continuation from long to short distance contributions. At the precision level
considered by them, however, there is a more important contribution from weak
magnetism that was not included by their calculation. The addition of the weak
magnetism contribution to the superallowed beta-decay radiative corrections
lowers $V_{ud}$ by 0.00023, which is compared with the increase 0.00007 of
Marciano and Sirlin and their error estimate $\pm 0.0002$.
