The resistivity of Ca-Al metallic glass is calculated as a function of temperature and composition. The diffraction model is used, including the partial dynamic structure factors. To account for the blurring of the Fermi surface we propose a new model which preserves the wave-packet character of the scattering electron. The results compare favorably with the experimental measurements available, indicating that the diffraction model is applicable also for high-resistivity systems. The use of t-matrix formulation of scattering is seen essential and the value of the Fermi wave vector to be used is shown to need careful consideration. The Fermi-surface blurring is found to affect the resistivity but the changes are not drastic. The origins of the large resistivity are seen to be in the strong scattering from Ca atoms, as expected, but also in the changes in the atomic and electronic structure.