Charles Koch offered Bernie Sanders an endorsement of sorts on Friday, writing that he agrees with the leftwing Democratic presidential candidate on issues of corporate welfare and criminal justice reform.

“The senator is upset with a political and economic system that is often rigged to help the privileged few at the expense of everyone else, particularly the least advantaged,” the billionaire political donor who has been one of Sanders’s frequent targets said in an op-ed for the Washington Post, adding: “I agree with him … I applaud the senator for giving a voice to many Americans struggling to get ahead in a system too often stacked in favor of the haves.”

Koch, one of the brothers behind Koch Industries, America’s second largest corporation, has long been an outspoken libertarian and critic of government intrusions on market forces – “even those that benefit us”, he wrote on Friday. Charles’s brother David ran for president on the Libertarian ticket in 1980.

Sanders has been an ardent critic of the Kochs for years, frequently invoking them in speeches about income inequality, corporate greed and campaign finance reform. The claim that the Koch brothers’ planned $900m of expenditures in the 2016 election is more than the Democratic or Republican parties will spend has been a standard part of Sanders’ stump speech on the campaign trail.

“As he campaigns for the Democratic nomination for president,” Koch writes, “Sanders often sounds like he’s running as much against me as he is the other candidates.”

The Koch brothers have bankrolled a number of rightwing and libertarian thinktanks such as the Cato Institute, the Heritage Foundation and the American Enterprise Institute. Koch money also played a large role in funding some of the groups that coalesced into the Tea Party in 2009.

Koch also noted his agreement with Sanders on the issue of criminal justice; the presidential candidate has called mass incarceration an “international embarrassment”, and pegged reform as “one of the most important things that a president of the United States can do”. Last year the Koch brothers signed on to a partnership with the Center for American Progress and other left-leaning thinktanks to found the Coalition for Public Safety aimed at reforming the US criminal justice system.

“Today, if you’re poor and get caught possessing and selling pot, you could end up in jail. Your conviction will hold you back from many opportunities in life. However, if you are well-connected and have ample financial resources, the rules change dramatically. Where is the justice in that?” Koch wrote.

But the column was not a true endorsement by any measure. “At this point you may be asking yourself, ‘Is Charles Koch feeling the Bern?’” the billionaire wrote. “Hardly.”

Koch went on to rail against federal programs like the war on poverty. “A bigger, more controlling, more complex and costlier federal government leaves the disadvantaged less likely to improve their lives,” Koch said.

Sanders, as a democratic socialist, has proposed dramatically ramping up federal spending on domestic programs for jobs, education, housing and poverty alleviation.