The present invention relates to a fluid composition intended for protecting the skin and/or hair against ultraviolet radiation, characterized by the fact that it comprises, in a cosmetically acceptable aqueous support, at least: (a) one photoprotective system capable of screening out UV radiation and (b) one 2-alkoxy-4-alkyl ketone phenol compound. The present invention also relates to the use of a 2-alkoxy-4-alkyl ketone phenol compound in a composition comprising, in a cosmetically acceptable medium, at least one photoprotective system capable of screening out UV radiation.