Spectral evolution of the optical transient accompanying GRB 120422A. The first two epochs show a smooth power-law-shaped continuum, which is characteristic of GRB afterglows. After the transient started re-brightening, the shape of the spectrum becomes redder. At 8.8 days after the GRB, the spectrum has clearly started to resemble that of a broad-lined SN. At 18.7 days, the transformation was complete, and the spectra look similar to other GRB-SNe. All spectra were shifted vertically by an arbitrary constant. They were rebinned (18 Å) to increase S/N for presentation purposes. We only display spectra with a large spectral range. Strong telluric lines (transparency <20%) are highlighted by the grey-shaded areas.