Lee looked forward to improving relationships with Mahathir Mohamad upon the latter's promotion to Deputy Prime Minister. Knowing that Mahathir was in line to become the next Prime Minister of Malaysia, Lee invited Mahathir (through Singapore President Devan Nair) to visit Singapore in 1978. The first and subsequent visits improved both personal and diplomatic relationships between them. Mahathir asked Lee to cut off links with the Chinese leaders of the Democratic Action Party; in exchange, Mahathir undertook not to interfere in the affairs of Malay Singaporeans.[citation needed]
In June 1988, Lee and Mahathir reached an agreement in Kuala Lumpur to build the Linggui dam on the Johor River.