The invention relates to a formulation comprising an ionic compound and a polyionic polymer. The invention more specifically relates to an improved formulation thereof, further comprising a copolymer. The improved formulation avoids phase-separation of colloidal particles comprising the ionic compound and the polyionic polymer. The formulation comprises a copolymer comprising two moieties A and B, wherein moiety A is polyionic in the pH conditions of the formulation, and moiety B is neutral in the pH conditions of the formulation.