The invention relates to a liquid-crystalline medium based on a mixture of polar compounds of positive dielectric anisotropy, containing at least one compound of the general formula I in which R1 and R2 are each, independently of one another, an alkyl or alkenyl radical having 1 to 12 carbon atoms which is unsubstituted, monosubstituted by CN or CF3 or at least monosubstituted by halogen, where one or more CH2 groups in these radicals may also, in each case independently of one another, be replaced by —O—, —S—, —CO—, —CO—O—, —O—CO— or —O—CO—O— in such a way that O atoms are not linked directly to one another and u is 1 or 2.