The paper discusses the morphological make-up of the converbial ending –mAdAn in adverbial clauses denoting temporal antecedence (before-clauses) and negative manner (without-clauses). In clauses denoting temporal antecedence, the converbial ending is optionally followed by the postposition önce ‘before’. The argument presented in the paper is that the converbial ending –mAdAn contains a negative marker –mA only in clauses where it is not followed by önce, while when the postposition follows, it contains the homophonous nominalizing suffix instead. Evidence for the claim comes on the one hand, from the fact that –mAdAn önce clauses do not license negative polarity items (but –mAdAn clauses do), and on the other, from the fact that –mAdAn önce clauses allow an addition of a negation marker to the converb (but –mAdAn clauses do not). Keywords: –mAdAn (önce), temporal adverbial clauses, converb, negation, NPI’s