The paper describes modification to Fm3–m (space group no. 225) lattice of aluminium based α-solid solution observed in Zn-Al alloys required to properly correlate quantitative data from X-ray diffraction analysis with results obtained from quantitative scanning electron microscopy image analysis and those predicted from Zn-Al binary phase diagram. Results suggests that 14 at.% of Zn as a solute atom should be introduced in crystal lattice of aluminium to obtain correct estimation of phase quantities determined by quantitative X-ray diffraction analysis. It was shown that this modification holds for Cu mould cast as well as annealed and water-cooled samples of Zn-3wt.%. Al and Zn-5wt.% Al.