The article reflects on the validity of a canonical marriage in the context of establishing by the nupturients the separation of property allowed by Polish law, i.e. the so-called prenup. The analysis of the norms of Polish law regulating the separation of property and the search for analogous norms in canon law aims at answering the question whether a prenup established before the wedding may constitute an exclusion of one of the aspects of the community of life and thus may have evidentiary value in the trial for the annulment of marriage? The analysis carried out led to the conclusion that it is not the prenup itself, but the intention with which the nuptuptial couple established it, that is important for the validity of the canonical marriage. Indeed, signing a prenup may sometimes be objectively justified, legitimate or even advisable. However, when a prenup is an expression of unwillingness to build marital unity, it will be a premise pointing to the invalidity of the marriage in the context of at least three titles: 1) as an exclusion of conjugal indissolubility (bonum sacramentum), 2) as an incapacity to undertake essential conjugal duties, and 3) as an exclusion of the good of the spouses (bonum coniugum).