Crystalline forms A and B of 5-methyl-pyridine-2-sulfonic acid [6-methoxy-5-(2-methoxy-phenoxy)-2-pyridin-4-yl-pyrimidin-4-yl]-amide of formula (I) are described, whereby form B is the most stable form. 5-methyl-pyridine-2-sulfonic acid [6-methoxy-5-(2-methoxy-phenoxy)-2-pyridin-4-yl-pyrimidin-4-yl]-amide also forms solvates with, for example, ethanol, acetone, tetrahydrofuran, methanol, isopropanol, 2-butanone and dichloromethane.