This article seeks to propose a solution to the oscillating interpretation of the application of Article 15 of Law 19.880 regarding the concept of «defenselessness», to resolve the admissibility of legal claims filed against proceeding acts issued by the Superintendence of the Environment (SMA). According to the proposal, the concept of defenselessness —understood as the concrete possibility of presenting allegations and defenses throughout the administrative procedure, and that these may influence the decision adopted in due time— must be linked to the right to challenge the decision. The two exceptions of Article 15 of Law 19.880 seek to prevent the application of the general rule on the basis of which no appeal may be lodged against proceeding acts from generating situations of defenselessness due to the absolute impossibility of appealing. Hence, the second exception (when the act generates defenselessness) is equivalent to the first one (when the act prevents the continuation of the procedure). Whilst in the first exception it is impossible to amend the defect by appealing against the terminal act, because the latter will not come into existence, in the second exception the impossibility arises from the consolidation of legal and factual situations generated by the intermedi-ate act. This approach is in line with the elements of interpretation recognized in our legal framework, makes the rule operative, and avoids the circularity that analyzing the admissibility requirements of the judicial claim based on its merit entails.