  We evaluate the effective mass of a scalar field phi coupled to thermal
plasma through Planck-suppressed interactions. We find it useful to rescale the
coupled fields so that all the phi-dependences are absorbed into the yukawa and
gauge couplings, which allows us to read off the leading order contributions to
the effective mass \tilde m_{phi} from the 2-loop free energy calculated with
the rescaled couplings. We give an analytical expression for \tilde m_{phi} at
a sufficiently high temperature in the case where phi is coupled to the MSSM
chiral superfields through non-minimal Kahler potential. We find that \tilde
m_{phi}^2 is about 10^{-3} H^2 \sim 10^{-2} H^2 for typical parameter sets,
where H is the Hubble expansion rate in the radiation-dominated era.
