The present invention relates to the xinafoate salt of N4-[(2,2-difluoro-4H-benzo[1,4]oxazin-3-one)-6-yl]-5-fluoro-N2-[3-(methylaminocarbonylmethyleneoxy)phenyl]-2,4-pyrimidinediamine. This compound is a suitable drug substance and is useful in the treatment of conditions including asthma.