The object of the present invention is a novel mandelate salt of a substituted tetracyclic tetrahydrofuran derivative according to Formula (I) the N-oxide forms and the stereochemically isomeric forms thereof, wherein R1 and R2 each independently are hydrogen or C1-6alkyl and R3 and R4 each independently are hydrogen or halogen. In the foregoing definitions C1-6alkyl defines straight and branched saturated hydrocarbon radicals having from 1 to 6 carbon atoms such as, for example, methyl, ethyl, propyl, butyl, 1-methylpropyl, 1,1-dimethylethyl, pentyl or hexyl. The novel mandelate salt is not light-sensitive and is far more stable than the prior art salts at room temperature, enhanced temperature and at relative high humidities and in aqueous media. Also disclosed are pharmaceutical compositions comprising mandelate salts according to the invention, mandelate salts according to the invention for use as a medicine, a process for preparing the mandelate salts according to the invention and the use of the mandelate salts and pharmaceutical compositions comprising mandelate salts according to the invention for the treatment or the prevention of CNS disorders, cardiovascular disorders and gastrointestinal disorders.