Two major Zimbabwe opposition figures signed a pact Wednesday pledging to work toward establishing a united front to challenge President Robert Mugabe in next year’s elections.

Morgan Tsvangirai, whose MDC-T party is the biggest opposition in parliament, and Joice Mujuru, a former vice president, described the memorandum of understanding as a significant step in their efforts to form a coalition.

Their two parties are exploring the possibility of working together in their bid to unseat the 93-year-old Mugabe, who has said he will contest the election. He has been in power since 1980, the end of British colonial rule. The once-prosperous Zimbabwe now faces cash shortages, high unemployment and rising frustration that led to nationwide protests last year.

More opposition parties are expected to join the alliance, Tsvangirai said.

“Even at the over-ripe old age of 93, President Mugabe knows that the country’s crisis is unsustainable. So we should stand together in unison and say enough is enough,” he told a joint press conference at his house in the capital, Harare.

The president has mocked opposition efforts to band together to defeat him, especially as some parties are troubled by internal fighting.

“We look with glee as they daily turn on each other, while pretending to chase a mirage they have termed ‘grand coalition,’ apparently unaware of the grand defeat that stares them in the face,” Mugabe told a meeting of the ruling ZANU-PF party on April. 7.

Mugabe, the world’s oldest head of state, fired Mujuru in 2014, accusing her of plotting to unseat him.

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