An installation for packaging a gaseous NO/N2 mixture into at least one container from a source (1) of gaseous NO and a source (2) of gaseous nitrogen is disclosed. The installation uses at least one filling system (3) comprising one or more filling stations (24) for gas containers (25). A first gas line (11) is fluidically connected to the source (1) of gaseous NO and to the filling system (3), and a second gas line (12) is fluidically connected to the source (2) of gaseous nitrogen and to the filling system (3). The first gas line (11) and the second gas line (12) each has a mass flow meter (4, 5), each mass flow meter (4, 5) being connected (14, 15) to a control device (6) collaborating with each mass flow meter (4, 5).