Disclosed herein is a maleic acid salt of 2-[2-((S)-3-dimethylaminopyrrolidin-1-yl)pyridin-3-yl]-5-ethyl-7-methoxy-4H-benz[d][1,3]oxazin-4-one (compound of formula (I)), crystals thereof, pharmaceuticals comprising said compound, methods for its preparation and uses thereof.