The invention relates to a polymorphic forms of (S)-3-(3-(1-methyl-2-oxo-5-(pyrazolo[1,5-a]pyridine-3-yl)-1H-imidazo[4,5-b]pyridine-3(2H)-yl)piperidin-1-yl)-3-oxopropanenitrile and their use as a therapeutic agent for the treatment of respiratory diseases.