Calculations of the energies of 4snp ^1,3P⁰ autoionising states of the magnesium atom are carried out using the model of configuration interaction. The energies of the 4snp ¹P⁰ states obtained coincide much better than the results obtained in earlier works with existing data, obtained in experiments on the photoabsorption of magnesium vapour in the far-ultraviolet region and in the study of the spectra of electrons ejected by autoionising states. In the case of 4snp ³P⁰ states, it is shown that the existing experimental classification of these states is not quite correct and has to be changed.