A constitutional referendum was held in Haiti on 30 January 1971. Before the referendum, the Haitian parliament had voted in favour of lowering the age limit for becoming president from 40 years to 20, as well as confirming Jean-Claude Duvalier, son of ailing dictator François Duvalier at 21 years of age, which would allow him to succeed his father.
Ballots were printed with the "yes" option already filled in. Although the official count was 2,391,916 in favour and no votes against, it was reported that there were two blank ballots and one "no" vote.
Fetching the article from Wikipedia…
Text from the Wikipedia article “Haitian constitutional referendum, 1971”, available under CC BY-SA 4.0.