A device for compensating for fluctuations in the concentration of a gaseous constituent in the fuel gas stream of a dynamically operated fuel cell system, has a buffer component arranged in the fuel gas stream, provided downstream of a component of the fuel cell system which is to be protected. The buffer component takes up the gaseous constituent from the fuel gas stream in the event of the partial pressure rising and releases the gaseous constituent back into the fuel gas stream in the event of the partial pressure dropping. According to the invention, the buffer component contains a material for the adsorption or absorption of the gaseous constituent that has a take-up capacity which is dependent on the partial pressure.