The present invention relates to an anhydrous solid composition for dyeing keratin fibres, in particular human keratin fibres such as the hair, comprising a particular chemical oxidizing agent and a polymer comprising at least one heterocyclic vinyl monomer. The present invention also relates to a packaging article containing said composition. The present invention also relates to processes for dyeing keratin fibres using said composition or said packaging article. Finally, the present invention relates to the use of said composition or of said packaging article for dyeing keratin fibres, and in particular human keratin fibres such as the hair.
