THE INVENTION CONCERNS AN AEROSOL FORMULATION SUITABLE FOR ADMINISTERING TO COPD PATIENTS BY MEANS OF A PRESSURIZED METERED DOSE INHALER (PMDI), COMPRISING GLYCOPYRRONIUM BROMIDE IN COMBINATION WITH FORMOTEROL. THE FORMULATION FURTHER COMPRISES A HFA PROPELLANT, A CO-SOLVENT, AND AN AMOUNT OF INORGANIC ACID SUFFICIENT TO STABILIZE BOTH THE GLYCOPYRRONIUM BROMIDE AND THE FORMOTEROL COMPONENTS. OPTIONALLY THE FORMULATION FURTHER COMPRISES BECLOMETASONE DIPROPIONATE.