  We present a simple method for including the oblateness of a rapidly rotating
neutron star when fitting X-ray light curves. In previous work we showed that
the oblateness induced by rotation at frequencies above 300 Hz produces a
geometric effect which needs to be accounted for when modelling light curves to
extract constraints on the neutron star's mass and radius. In our model X-rays
are emitted from the surface of an oblate neutron star and propagate to the
observer along geodesics of the Schwarzschild metric for a spherical neutron
star. Doppler effects due to rotation are added in the same manner as in the
case of a spherical neutron star. We show that this model captures the most
important effects due to the neutron star's rotation. We also explain how the
geometric oblateness effect can rival the Doppler effect for some emission
geometries.
