The Mississippi Department of Education says a $1,500 raise for teachers will cost $18.5 million more than it originally told lawmakers.

The department made the announcement Monday, months after local superintendents discovered a shortfall caused by the department’s ignorance of how teachers were classified in its computer system.

Lawmakers allotted $58 million for the raise that began July 1, based on it going to 31,000 teachers. But the department didn’t count 10,000 other teaching positions that officials thought were federally funded. Instead, those positions are state-funded, and Mississippi must absorb the costs.

Legislators pledge to pay the remainder of the full $77 million when they convene in January after elections. State Superintendent Carey Wright has said the department will give local school districts enough money to cover costs until then.