A hydrate of 5-[4-[2-(N-methyl-N-(2-pyridyl)amino)ethoxy]benzyl]thiazolidine-2,4-dione, maleic acid salt, characterized in that it: (i) comprises water in the range of from 0.2 to 1.1% w/w; and (ii) provides an infrared spectrum containing peaks at 764 and 579 cm^-1; and/or (iii) provides an X-ray powder diffraction (XRPD) pattern substantially as set out in FIG. II; a process for the preparation of such a compound, a pharmaceutical composition containing such a compound and the use of such a compound or composition in medicine.