Aerosol solution compositions intended for use with a pressurized metered dose inhaler, comprising glycopyrronium bromide and formoterol, or a salt thereof or a solvate of said salt, optionally in combination with one or more additional active ingredients, and stabilized by a selected amount of a mineral acid, exhibit improved stability when contained in a can internally coated by a resin comprising a fluorinated ethylene propylene (FEP) polymer.