The author examines the persistence of discriminatory inheritance practices that exclude daughters from inheriting land, houses, and other unmovable property from their parents among urban Toba Batak people in Indonesia. These practices persist in spite of national legal policy mandating equal rights for men and women. Drawing on Sally Falk Moore's concept of the semi-autonomous social field, the essay argues that traditional forms of inheritance are maintained through the marga-association, which brings together people who share the same name and affirms principles of patrilineal descent as the defining characteristics of Batak identity in contemporary urban settings. Both men and women voluntarily affirm these principles, arguing that because a woman becomes part of her husband's lineage at the time of marriage, she is not entitled to her father's estate. The marga-association thus acts as an insulating mechanism between state law and traditional (adat) law, protecting the latter from the legal transformations imposed by the state.