The field of the invention relates to stable oral dosage forms comprising, (a) cis-adamantane-2-spiro-3'-8'-[[[(2'-amino-2'-methylpropyl) amino]carbonyl]-methyl]-l',2',4'-trioxaspiro[4.5]decane hydrogen maleate (Active compound I); (b) piperaquine; and (c) one or more pharmaceutically acceptable excipients; and processes for their preparation, especially wherein the dosage form is prepared by a dry process.