We present a theoretical expression for the components of the Lagrangian displacement field xi for a rotating, pulsating star, taking into account the effect of the Coriolis force. We re-emphasize that for a rotating star xi cannot be described by a single spherical harmonic; correction terms proportional to the ratio OMEGA/omega of the rotation and pulsation frequencies have to be taken into account. We show that this first-order correction to a mode with degree l and azimuthal number m consists of two toroidal terms, one with degree l - 1 and one with degree l + 1, and one spheroidal term with degree l, all sharing azimuthal number m. A second-order approximation, which would also take into account the effect of the centrifugal force, was not attempted, because of the extreme complexity of the problem if spherical symmetry does not apply. Our expressions thus apply to a monoperiodic pulsation with a period significantly shorter than the rotation period, i.e. for p-modes or low-order g-modes, or for high-order g-modes in slow rotators.