BRUNSWICK, Maine (AP) — Independent U.S. Sen. Angus King has returned a donation from Exxon Mobil after his Democratic challenger pressed him on the gas corporation’s contribution during a debate.

Maine Public Radio reports candidate Zak Ringelstein asked King if he would distance himself from the fossil fuel industry and return the $5,000 donation during a Senate debate Tuesday. The question came as Ringelstein explained his support for a plan to convert to 100 percent renewable energy by 2035.

King agreed to give the donation back, but said Ringelstein’s question was misleading. He added that he discloses all his contributions and didn’t know about the Exxon Mobil donation.

According to the Center for Responsive Politics, King has received over $124,000 from natural resource groups. Most of the money has flowed from renewable energy groups.