Colorado Gov. John Hickenlooper called lawmakers back to the state Capitol to fix a tax error which cost cannabis businesses in Denver hundreds of thousands of dollars a month in cannabis revenue.

The special session is scheduled for Oct. 2, while the problem was discovered near the end of June, one month after the 2017 legislative session was scheduled to close. It will be the first time in five years Hickenlooper had called a special session, when he typically deferred to lawmakers on legislative matters during his terms in office.

The error originated from Senate Bill 267, a spending measure which overhauled hospital funding and rewrote the state’s cannabis tax law. The bill eliminated a 2.9 percent tax on social cannabis in favor of a special sales tax hike on the plant from 10 to 15 percent.

The rewrite mistakenly cut funding from the Regional Transportation District (RTD), the Scientific Facilities District and other organizations and blocked them from collecting social cannabis taxes they levied before the bill took effect in July.

“Now that the governor has called a special session to resolve this issue, we owe it to the affected special districts and the people they serve to correct this mistake as quickly and efficiently as possible,” House Speaker Crisanta Duran, D-Denver, said in a statement. “We’ll be ready to go in October.”

Under the Colorado state constitution, lawmakers are required to gather when a special session is called but they are not required to take action.