The corrosion inhibitor blend of at least one corrosion inhibitor base (which may be a Mannich reaction product), a solvent selected from the group consisting of C.sub.1 acids and ester and salt derivatives thereof, and optionally a surfactant, has been found to be effective as a corrosion inhibitor for metals in acid media, particularly fluids containing halogen acids. The corrosion inhibitor has improved performance over similar or identical corrosion inhibitor compositions where an alcohol such as methanol is used as a solvent. Suitable, non-limiting possibilities for the solvent include, but are not necessarily limited to formic acid, formate salts, methyl formate, ethyl formate, benzyl formate, formate salts of amines, inorganic formate, and mixtures thereof.