Gov. John Hickenlooper on Thursday called lawmakers back to the Capitol to fix a bill-drafting error that has been costing Denver-based institutions hundreds of thousands of dollars a month in marijuana revenue.

The special session set to start Oct. 2 will be the first in five years for Hickenlooper and the General Assembly, an extraordinary step for a governor who typically has deferred to lawmakers on legislative matters during his two terms.

“After hearing about the potential impact on citizens around the state, it is clear that this problem is best solved as soon as possible,” Hickenlooper said in a statement announcing his executive order, capping a day of speculation about his plans.

The problem affecting the Regional Transportation District and other organizations was discovered near the end of June — a little more than a month after the 2017 legislative session was gaveled to a close. In the weeks that followed, the governor’s office said it was exploring ways to fix it without calling a special session.

Ultimately, the governor decided legislation was needed — and that that legislation couldn’t wait until lawmakers were scheduled to return in January.

“There’s a serious amount of money involved and consequences,” Hickenlooper said earlier Thursday in an interview with The Denver Post. “We are trying to figure out: Does it make sense? Can we make a difference?”

Hours before the governor announced his decision, the General Assembly’s top Republican lawmaker said he remained unconvinced that a special session is warranted.

“We’ve yet to hear the governor present a strong, iron-clad case for why this can’t wait until next session, which is now just four months away,” Senate President Kevin Grantham said in a statement.

Later in the evening, another top Republican complained that he didn’t hear from the governor’s office until after the decision had been announced.

“This is not the way government should work in Colorado,” said Senate Pro Tem Jerry Sonnenberg of Sterling. He’s one of the sponsors of the legislation that’s now in dispute. “Calling a special session without an understanding of the game plan, or proper consultation with the legislators involved, is an irresponsible use of taxpayer dollars.”

Meanwhile, House Speaker Crisanta Duran, the top Democrat in the opposite chamber, offered her caucus’s support.

“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,” Duran, of Denver, said in a statement. “We’ll be ready to go in October.”

The error stemmed from Senate Bill 267, the wide-ranging spending measure that overhauled a state hospital funding program and rewrote the state’s pot tax law, eliminating a 2.9 percent tax on recreational pot in favor of a hike in the special sales tax on weed from 10 to 15 percent.

But the rewrite of the law mistakenly cut funding from RTD, the Scientific and Cultural Facilities District and other organizations, blocking them from collecting recreational pot taxes that they had levied before the bill took effect July 1.

The Denver arts and cultural district includes dozens of organizations, such as the Denver Zoo and Denver Museum of Nature & Science.

RTD officials previously told The Post that the regional transit service could stand to lose as much as $3 million if the pot tax glitch wasn’t fixed before the next legislative session begins in January.

“We never intended this,” said House Majority Leader KC Becker, D-Boulder, speaking of the bill she co-sponsored. “There were dozens upon dozens of people that reviewed this draft” but didn’t catch the error before it was too late.

Nate Currey, a spokesman for RTD, said the district was “grateful” for the governor’s decision.

“I think everybody recognizes that it’ll be something that’ll be a quick fix,” he said.

Earlier this year, Hickenlooper flirted with the idea of calling lawmakers back to the Capitol to hammer out deals on transportation funding, health care and the Colorado Energy Office, whose funding sunsets this summer. But he ultimately backed off the idea when Republican lawmakers balked.

Under the state constitution, lawmakers are required to convene a special session when called, but they don’t have to take action. The last time Hickenlooper called a special session was 2012, when lawmakers were called back to debate a civil unions bill and other unfinished business.