The formation of haloes of the M 31 and NGC 5128 galaxies through mergers of fragments is considered. It is found that the accretion of unenriched gas plays an important role in the chemical evolution of fragments before their merger. We make the assumption that the haloes of the M 31 and NGC 5128 galaxies could be formed by merger of two massive fragments with mass ratios 1:1 and 1:2.57, respectively. This allows us to reproduce the observed halo metallicity distribution function of the galaxies quite well.