Crystalline form, Form N-1, of [(1R), 2S]-2-aminopropionic acid 2-[4-(4-fluoro-2-methyl-1H-indol-5-yloxy)-5-methylpyrrolo[2,1-f][1,2,4]tr- iazin-6-yloxy]-1-methylethyl ester (Compound I) is provided. Also provided are a pharmaceutical composition and an oral dosage form comprising the Form N-1 of Compound I as well as a method of using the Form N-1 of Compound I in the treatment of cancer and other proliferative diseases.