The invention relates to 5-cyano-3-methyl-pyridine-2-carboxylic acid [3-((3R,6R)-5-amino-3,6-dimethyl-6-trifiuoromethyl-3,6-dihydro-2H-(1,4)oxazin-3-yl)-4-fluoro-phenyl))-amide in crystalline form, to its preparation, its medical use and to medicaments comprising said compound in crystalline form for use in the treatment of Alzheimer's disease.