The language contact between Basque and Spanish in the Basque Autonomous Community (BAC) gives rise to the production of specific linguistic features such as non-standard gender agreement (N-SGA). N-SGA in BAC Spanish has been traditionally attributed to elder Basque native speakers without much access to education, but this affirmation is not based on any empirical study. In addition, although several scholars have explored N-SGA in other language contact situations, there is no agreement on the linguistic factors that favor this production. Taking this knowledge gap as the point of departure, the present study explores 73 individual sociolinguistic interviews by a diverse population from the BAC in order to delimit (i) the community that produces N-SGA and (ii) the linguistic factors that condition it. Results follow Basterretxea Santiso’s (2022, “A triangulation study on gender agreement in Spanish by native Basque speakers.” Revista Española de Lingüística (RSEL) 52(1): 7–37) suggestion that N-SGA in BAC Spanish is present across generations: it is a well-established feature present in BAC Spanish as a result of language contact. Results also support the existence of a local gender agreement system that depends on the gender of the controller, inflectional form, number, distance, and whether the target is a clitic or adjective.