Substituted triazolopyrimidines of the formula I in which the substituents are as defined below: R1 is alkyl, haloalkyl, cycloalkyl, halocycloalkyl, alkenyl, haloalkenyl, cycloalkenyl, halocycloalkenyl, alkynyl, haloalkynyl or phenyl, naphthyl, or a five- or six-membered saturated, partially unsaturated or aromatic heterocycle comprising one to four heteroatoms from the group consisting of O, N and S, R2 is hydrogen or a group R1, R1 and R2 together with the nitrogen atom, to which they are attached, may also form a five- or six-membered heterocyclyl or heteroaryl which is attached via N and which may comprise one to three further heteroatoms from the groups consisting of O, N and S as ring member and/or may be substituted according to the description; L is fluorine, chlorine or methyl; X is cyano, C1-C4-alkyl, C1-C4-alkoxy or C1-C2-haloalkoxy, where X is not methyl if R1 and R2 together are n-pentylene or 3-methyl-n-pentylene and L is fluorine, or R1 and R2 together are 3-methyl-n-pentylene and L is chlorine; processes and intermediates for preparing these compounds, compositions comprising them and their use for controlling phytopathogenic harmful fungi.