In 1949, he was also the leader of the delegation at the Roem – van Roijen Agreement, that discussed Indonesia's borders, and which was signed on May 7, 1949.
Pada tahun 1949, ia juga pemimpin delegasi di Perjanjian Roem-Roijen, yang membahas batas Indonesia, dan ditandatangani pada tanggal 7 Mei 1949.