  The Planck satellite detectors are calibrated in the 2015 release using the
"orbital dipole", which is the time-dependent dipole generated by the Doppler
effect due to the motion of the satellite around the Sun. Such an effect has
also relativistic time-dependent corrections of relative magnitude 10^(-3), due
to coupling with the "solar dipole" (the motion of the Sun compared to the CMB
rest frame), which are included in the data calibration by the Planck
collaboration. We point out that such corrections are subject to a
frequency-dependent multiplicative factor. This factor differs from unity
especially at the highest frequencies, relevant for the HFI instrument. Since
currently Planck calibration errors are dominated by systematics, to the point
that polarization data is currently unreliable at large scales, such a
correction can in principle be highly relevant for future data releases.
