The effect of the Jahn-Teller coupling on the shape of the d ↔ d transition of a 3d⁶ ion in a cubic crystal is calculated on a simplified model in which the kinetic energy of the nuclei is neglected in the excited state. The result is applied to Fe²⁺ in MgO by the use of a modified Debye model, using data from compressional experiments. The predicted splitting of the d ↔ d transition is about half that actually observed. The reduction of the ground state g value by the Jahn-Teller coupling is small.