A method for improving the ferrous corrosion-preventing characteristics of a fuel comprises combining an additive having a chemical structure comprising a 6-membered aromatic ring sharing two adjacent aromatic carbon atoms with a 6- or 7-membered saturated heterocyclic ring, the 6- or 7- membered saturated heterocyclic ring comprising a nitrogen atom directly bonded to one of the shared carbon atoms to form a secondary amine and an atom selected from oxygen or nitrogen directly bonded to the other shared carbon atom, the remaining atoms in the 6- or 7- membered heterocyclic ring being carbon with the fuel. The additive may also be used for preventing ferrous corrosion in a system which comprises a fuel, such as a fuel system in a vehicle.