(Bloomberg) — Saudi mothers will be able to apply for passports for children in their custody and approve travel abroad under new guidelines. The changes, detailed on the website of Saudi Arabia’s General Directorate of Passports on Monday, spell out how a major policy change earlier this month — which allowed women over 21 to leave the country without a male relative’s permission from the end of August — will work in practice.

Saudi women’s rights activists have campaigned for years against the kingdom’s guardianship system, which rendered women legal dependents of a male relative throughout their lives — typically a father or husband, but sometimes a brother or son.

Crown Prince Mohammed bin Salman has put loosening social restrictions at the heart of his economic transformation plan for Saudi Arabia, which relies on diversifying away from oil and attracting foreign investment.

The new guidelines specify that men and women over the age of 21 can obtain passports and travel without a guardian’s approval. Those who are under 21 won’t need permission if they are either married, traveling to study on a government scholarship or heading overseas on “official duties.”

In another key shift, Saudis under 21 whose fathers are dead can get approval to travel from their mother, as opposed to another male relative — though the guidelines still appear to give priority to fathers if both parents are alive.

In cases of divorce, whichever parent has custody can apply for passports and issue travel permissions for their children. Previously that right was restricted to men, leaving some mothers in the lurch.