Multiparameter stacking has become a standard tool for seismic reflection data processing. Although different traveltime operators exist, whose accuracy depends on the offset and reflector curvature, neither of these can account for anisotropy. We introduce a new stacking operator, which is derived from evaluating Snell's law at a locally spherical interface in an anisotropic medium. Examples show that the new operator performs well for the whole range of reflector curvatures from nearly planar reflectors to the diffraction limit.