The present disclosure relates to solid forms of N-{[2'-(2,6-difluoro-3,5-dimethoxyphenyl)-3'-oxo-2',3'-dihydro-1'H-spiro[cyclopropane-1,4'-[2,7]naphthyridin]-6'-yl]methyl}acrylamide, methods of preparation thereof, and intermediates in the preparation thereof, which are useful in the treatment of the FGFR-associated or mediated diseases such as cancer.