A liquid preparation of a paper dye comprising a) 15 to 50% by weight of the dye of the formula CuPc[SO2NH(CH2)3N(CH3)2]2 to 3[SO3H]1 to 2 (1), in which CuPc represents copper phthalocyanine, or the alkali metal salt of (1), b) 5 to 15% by weight of ∈-caprolactam, c) 1 to 8% by weight of formic acid, d) 1 to 7% by weight of benzyl alcohol, e) 0 to 3% by weight of a lower aliphatic organic acid, f) 0 to 5% by weight of an inorganic salt and g) water, to complete to 100% by weight, a process for the production of said preparation and the use thereof for dyeing, in particular dyeing of paper.