Disclosed is crystalline Form A of 6-(cyclopropanecarboxamido)-4-((2-methoxy-3-(1-methyl-1H-1,2,4- triazol-3-yl)phenyl) amino)-N-(methyl-d3)pyridazine-3-carboxamide. Form A is a neat crystalline form. Characterization data for Form A are disclosed.Se describe la forma cristalina A de la 6-(ciclopropanocarboxamido )-4-((2-metoxi-3-(1-metil-1H-1,2,4-triazol-3-il)fenil)amino)-N-(m etil-d3)piridazin-3-carboxamida. La forma A es una forma cristalina pura. Se describen los datos de caracterización para la forma A.