A trilateral meeting of Prime Ministers of Bulgaria, Serbia and Hungary is to take place in the Black Sea city of Burgas on Tuesday, the government's press office has said.
The arrival of Hungary's Prime Minister Viktor Orbán was agreed last week in a phone conversation.
Serbian Prime Minister Aleksandar Vučić will depart immediately after the meeting on September 13.
Orbán is due to stay and inspect the border fence between Bulgaria and Turkey, at Lesovo crossing point, on the next day.
Hungary's head of government was already on an official visit to Belgrade earlier in September, with the migrant crisis being high on the agenda.
The trilateral meeting is expected to focus on the same issue.
Sofia News Agency