The present invention relates to new crystalline forms of the inhibitor, 5-fluoro-3-phenyl-2-[(S)-1-(9H-purin-6-ylamino)-propyl]-3H-quinazoline-4-one the present invention also relates to methods for preparing the new crystalline forms of 5-fluoro-3-phenyl-2-[(S)-1-(9H-purin-6-ylamino)-propyl]-3H-quinazolin-4-one, pharmaceutical compositions containing the new crystalline forms thereof, and uses thereof for the treatment and/or prevention of diseases such as chronic lymphocytic leukemia and indolent non-Hodgkins lymphoma.