The present invention relates to a specific salt of a dihydropteridione derivative, namely the trihydrochloride salt of the compound N-[trans-4-[4-(cyclopropylmethyl)-1-piperazinyl]cyclohexyl]-4-[[(7R)-7-ethyl-5,6,7,8-tetrahydro-5-methyl-8-(1-methylethyl)-6-oxo-2-pteridinyl]amino]-3-methoxy-benzamide, to its crystallisation in the form of an hydrate with water, to a process for the manufacture thereof, and to the use thereof in a pharmaceutical composition.