Nigeria will pay an extra $4 billion to service its debt if the Senate blocks a plan to restructure government loans from the central bank, according to President Muhammadu Buhari.

The upper chamber of parliament in Africa’s largest economy last week suspended a session to consider Buhari’s request to convert 22.7 trillion naira ($50.6 billion) in advances from the Central Bank of Nigeria into bonds repayable over 40 years. Some lawmakers said the borrowing is unconstitutional.

“Failure to grant the securitization approval will however cost the government about 1.8 trillion naira in additional interest in 2023,” Buhari told the National Assembly on Tuesday, according to an emailed statement from his spokesman, Femi Adesina. Buhari’s administration has negotiated a more favorable interest rate and longer repayment period with the central bank, the statement said.

Buhari made the remarks while signing this year’s 21.8 trillion naira budget that was approved last week by both the Senate and House of Representatives. The president will step down at the end of his second term following elections due to be held next month.