The Democratic Republic of Congo’s two leading opposition presidential challengers are discussing choosing a single candidate to run in elections scheduled for December.

Moise Katumbi, a former ally of the current head of state, Joseph Kabila, and Felix Tshisekedi, the leader of Congo’s oldest and largest opposition party, issued a joint statement Thursday.

They said their “teams are hard at work developing a common program and when the time comes the designation of a sole candidate at the next presidential election.” Both men had previously announced separate bids to succeed Kabila.

Congo, which hasn’t had a peaceful transfer of power since independence in 1960, was supposed to hold elections in November 2016 at the end of Kabila’s constitutionally limited second term. The electoral commission postponed the vote, citing financial and logistical constraints, causing protests that have been suppressed by security forces.

Polls are now scheduled for Dec. 23 and Kabila’s ruling coalition has repeatedly said the electoral process underway is irreversible. But the president’s refusal to rule himself out or appoint a candidate has fueled speculation he’ll seek to change or reinterpret the constitution to run again -- or delay the vote.

Katumbi, the former governor of copper-rich Katanga province, has been in self-imposed exiled since May 2016, soon after he split with Kabila and announced an intention to replace his one-time boss. A month later he was convicted in absentia for illegally selling a property, while two other investigations remain open -- including allegations he violated Congo’s ban on dual citizenship. Katumbi denies the allegations, which he says are politically motivated.

Presidential candidates are required to submit their applications between July 25 and Aug. 8, according to the current schedule.