The invention relates to a primer, comprising a mixture dissolved or dispersed in one or more solvents, the mixture composed of a copolymer obtained through copolymerization, preferably free-radical copolymerization, of vinylcaprolactam and/or vinylpyrrolidone, and one or more of the following monomers: a) an acrylic acid ester of a linear primary alcohol containing 2 to 10 carbon atoms in the alkyl group of the alcohol, b) an acrylic acid ester of a branched, non-cyclic alcohol having 4 to 12 carbon atoms in the alkyl group of the alcohol, c) acrylic acid, one or more organofunctional silanes. Such primer provides reliable and excellent adhesion between pressure-sensitive adhesive tapes and hydrophilic surfaces, in particular glass. The adhesion-promoting effect is retained even when the primer additionally contains functional fillers.