Last minute preparations are underway for voters in the Eastern European country of Ukraine to select their next president on Sunday.

They will choose between President Petro Poroshenko and Volodymyr Zelenskiy, a standup comic who plays a fictional president in a popular television series.

The 41-year-old Zelenskiy, who has no political experience, is heavily favored to defeat Poroshenko, polls show. Zelenskiy’s once long-shot bid for the presidency gained momentum amid voter frustration over corruption, economic woes and an ongoing conflict in the country’s east.

Poroshenko tried to energize his supporters at a rally Friday in Kiev’s Independence Square, just hours before the candidates square off in a nationally televised debate in the city’s Olympic Stadium. The 51-year-old president told several thousand supporters Zelenskiy would be exploited by Russian President Vladimir Putin if he were elected and said a Zelenskiy win would derail Ukraine’s chances of integrating into the European Union (EU).

Russia annexed Ukraine’s Crimean peninsula in 2014 and the country has since been entangled in a war with Russian-backed separatists in the eastern part of the country.

Zelenskiy has shunned traditional political campaigning, largely avoiding media interviews and touring the country with his comedy show instead. When he has spoken with the media, he has advocated for closer ties with the EU and NATO. He has also called for greater efforts to reintegrate the rebels in the east into the country.