The present invention is concerned with an improved process for the preparation of pyrido[2,1-a]isoquinoline derivatives of formula I wherein R1, R2 and R3 are each independently hydrogen, halogen, hydroxy, lower alkyl, lower alkoxy or lower alkenyl, wherein lower alkyl, lower alkoxy and lower alkenyl may optionally be substituted by lower alkoxycarbonyl, aryl or heterocyclyl, and the pharmaceutically acceptable salts thereof. The invention also relates to two crystalline forms of (2S,3S,11b S)-1-(2-amino-9,10-dimethoxy-1,3,4,6,7,11b-hexahydro-2H-pyrido [2,1-a]isoquinolin-3-yl)-4(S)-fluoromethyl-pyrrolidin-2-one dihydrochloride, which are form A and form B and to an amorphous form of said compound.