On working with an X-ray powder diffractometer, due to practical difficulties, the surface of the specimen some times is not accurately placed on the working plane of the goniometer. This disagreement produces an asymmetric broadening of the diffraction line profile, and also a shift in the peaks positions. In this work we expose some considerations about the way each diffracted beam fulfils the Bragg’s law, addressed to its possible application for correcting the 2θ shifts caused by the specimen-displacement error of polycrystalline samples.