The present invention relates to crystal modifications of N-{(2R)-2-[({[3, 3-dibutyl-7-(methyl-thio)-1, 1-dioxido-5-phenyl-2, 3, 4, 5-tetrahydro-1, 5-benzothiazepin-8-yl]oxy}acetyl)amino]-2-phenylethanolyl}glycine (elobixibat), more specifically crystal modifications I, IV, MeOH-1, EtOH-1, 1-PrOH-1 and 2-PrOH-1. The invention also relates to a process for the preparation of these crystal modifications and to a pharmaceutical composition comprising crystal modification IV.