This invention relates to a crystalline form of (10R)-7-amino-12-fluoro-2,10,16-trimethyl-15-oxo-10,15,16,17-tetrahydro-2H-8,4-(metheno)pyrazolo[4,3-h][2,5,11]benzoxadiazacyclo-tetradecine-3-carbonitrile (lorlatinib) free base hydrate (Form 24). This invention also relates to pharmaceutical compositions comprising Form 24, and to methods of using Form 24 and such compositions in the treatment of abnormal cell growth, such as cancer, in a mammal.