Marriage annulment in Indonesia lies at the intersection of national civil law and the religious law governing the spouses, particularly for Catholics whose marriages are also subject to the Codex Iuris Canonici (KHK). Although marriage annulment differs fundamentally from divorce, its application in Indonesian courts remains insufficiently examined, especially in cases involving Catholic marriages. This study analyzes Decision Number 39/PDT.P/2021/PN.PSB, in which the Pasaman Barat District Court granted a Catholic couple’s petition for marriage annulment, to assess whether the court’s reasoning is consistent with Indonesian Marriage Law and the substantive doctrine of canonical nullity. Using normative legal research with statutory and case approaches, the study examines the decision alongside relevant legislation, the KHK, and scholarly literature. The findings show that while the court referred to canonical provisions, its reasoning primarily relied on Article 2 of Law Number 1 of 1974 on Marriage, as amended by Law Number 16 of 2019, rather than the substantive grounds for nullity established under the KHK. This demonstrates a conflation between civil marriage validity and canonical marriage validity, resulting in doctrinal inconsistency. The study concludes that judges should clearly distinguish civil and canonical concepts of marriage validity when adjudicating religiously grounded annulment petitions to ensure greater legal certainty and doctrinal coherence.