The invention relates to a synergistic mixture comprising between 1 and 99.9 wt. % of compounds having structural elements (I) in which the free valencies on the oxygen atom and on the nitrogen atom can be combined to form a five-membered, six-membered, or seven-membered ring and the benzene nucleus can still carry substituents on at least one of the free positions, and between 0.1 and 99 wt. % of sulphurous organic compounds having an anti-oxidant action. The synergistic mixture is suitable as a stabiliser for stabilising inanimate organic material, especially mineral oil products and fuels, against the effects of light, oxygen, and heat.