The present invention provides a salt form and compositions thereof, which are useful as an inhibitor of EGFR kinases and which exhibits desirable characteristics for the same. Examples include hydrobromide and bis-besylate salts of N-(3-(2-(4-(4-acerylpiperazin-1-yl)-2-methoxyphenylamino)-5-(trifluoromethyl)pyrimidin-4-ylamino)phenyl)acrylamide). The salts and their polymorphs are evaluated for their properties such as stability, solubility, and pharmacokinetics.
