Chromium precipitates generated by controlled internal reduction of (Al, Cr)2O3polycrystals are used as indicator for the occurrence of DIGM (diffusion-induced grain boundary migration) in this material. Asymmetric precipitate-free zones limited at one side by a grain boundary are observed inside the reduction scale. This observation is ascribed to diffusion induced migration of the grain boundaries, defect relaxation in the oxygen potential gradient being the driving force.