  We fit the Doppler profiles of the He-like triplet complexes of \ion{O}{7}
and \ion{N}{6} in the X-ray spectrum of the O star $\zeta$ Puppis, using
XMM-Newton RGS data collected over $\sim 400$ ks of exposure. We find that they
cannot be well fit if the resonance and intercombination lines are constrained
to have the same profile shape. However, a significantly better fit is achieved
with a model incorporating the effects of resonance scattering, which causes
the resonance line to become more symmetric than the intercombination line for
a given characteristic continuum optical depth $\tau_*$. We discuss the
plausibility of this hypothesis, as well as its significance for our
understanding of Doppler profiles of X-ray emission lines in O stars.
