An antifreeze concentrate for cooling systems in fuel-cell drives which gives ready-to-use aqueous coolant compositions having a conductivity of at most 50 .mu.S/cm, based on alkylene glycols or derivatives thereof and containing one or more five-membered heterocyclic compounds (azole derivatives) having 2 or 3 hetero atoms from the group consisting of nitrogen and sulfur, which contain no or at most one sulfur atom and which may carry a fused aromatic or saturated six-membered ring.