Japan’s government led by arch-conservative Prime Minister Sanae Takaichi – the country’s first female prime minister – wants to secure the future of the monarchy through adoption of male descendants from former imperial branch families.

The law, however, continues to bar women from ascending the throne.

Parliament on Friday has approved a revision of the Imperial Household Law, the first major overhaul of the legislation since it came into force in 1947.

The changes allow male members of former collateral branches of the imperial family to be readmitted. Those branches lost their imperial status after World War II and their members have since lived as private citizens.

The move comes as the world’s oldest hereditary monarchy is gradually running out of heirs.

Currently, only three candidates are theoretically available as successors to Emperor Naruhito, 66: the Emperor’s brother, Crown Prince Akishino, 60; Akishino’s 19-year-old son Prince Hisahito; and Naruhito’s uncle Prince Hitachi – who is already 90.

If Prince Hisahito, the only male of the youngest generation of the imperial family, does not have a son, a male descendant of an adopted former imperial family member could inherit the Chrysanthemum Throne under the revised law. The legislation continues to restrict succession to male descendants in the paternal imperial line.

Princess Aiko barred from throne

The first significant revision of the Imperial Household Law since 1947 shows “that gender equality is not among the priorities,” Sven Saaler of Sophia University in Tokyo said. “A woman on the imperial throne has been pushed even further into the distance by the legal amendment,” he told dpa.

Many people in Japan would like to see Princess Aiko, 24 – the emperor’s only child with his wife Masako – become empress.

The revised law also allows female members of the imperial family to retain their imperial status after marrying commoners. However, their spouses and children will not become members of the imperial family and will remain private citizens.

Experts have questioned whether the changes will resolve the succession issue. Japan’s imperial family currently has just 16 members.