Ong Ah Chuan v. Public Prosecutor is a landmark decision delivered in 1980 by the Judicial Committee of the Privy Council on appeal from Singapore which deals with the constitutionality of section 15 of the Misuse of Drugs Act 1973 (No. 5 of 1973) (now section 17 of the Misuse of Drugs Act (Cap. 185, 2008 Rev. Ed.)) ("MDA"), and the mandatory death penalty by the Act for certain offences. The appellants contended that the presumption of trafficking under section 15 of the MDA violated Article 9(1) of the Constitution of the Republic of Singapore (1980 Reprint) (now the Singapore Constitution (1985 Rev. Ed., 1999 Reprint)) and that the mandatory death penalty was arbitrary and violated Article 12(1) of the Constitution.