The invention relates to a crystalline form of (S)-2-(8-((5-chloropyrimidin-2-yl)(methyl)amino)-2-fluoro-6,7,8,9-tetrahydro-5H-pyrido[3,2-b]indol-5-yl)acetic acid, processes for the preparation thereof, pharmaceutical compositions comprising said crystalline forms, pharmaceutical compositions prepared from such crystalline forms, and their use as a medicament, especially as CRTH2 receptor modulators.