It is shown that at moderately high Bragg angles the shifts Δ(2θ) of the peaks of x-ray diffraction maxima resulting from geometrical aberrations of the apparatus are to a first approximation the same as those of the centroids. A second approximation to Δ(2θ) is obtained by adding Vh'"/2h" to the centroid shift, where V is the variance of the aberration and h" and h'" are the second and third derivatives of the observed line profile at its maximum. Forms of the correction suitable for practical application are discussed.The peak shifts resulting from dispersion and the Lorentz factor cancel to a first approximation. Physical aberrations, such as absorption, that multiply the line profile I(λ)dλ by a factor f(λ) depending on wavelength, shift the peak by approximately Δ(2θ)=-2f'Itanθ/λfI", where f, f', I, I" are the values of the functions and their derivatives at the peak.