The present disclosure relates to a crystalline form of 2-((4S)-6-(4-chlorophenyl)-1-methyl-4H-benzo c]isoxazolo 4,5-e]azepin-4-y- l)acetamide, which is useful as an inhibitor of bromodomain-containing proteins. The present disclosure also provides pharmaceutically acceptable compositions comprising the crystalline form and methods of using said compositions in the treatment of various disorders.