Warren Buffett has said he's willing to "put money" on Hillary Clinton winning the 2016 presidential race. Turns out, he really meant it.

The Oracle of Omaha gave the maximum donation allowed to Ready for Hillary last quarter, his first-ever check to the sort of independent political groups that he's scorned in the past. Buffett, who is the third richest man in the world, gave $25,000, the most any individual can donate under the committee's self-imposed cap, according to a person familiar with Ready for Hillary's post-election financial disclosure report. The group has raised more than $11 million to finance its efforts to lay the groundwork for a Clinton presidential campaign. Their latest report is due to be filed with the Federal Election Commission by midnight Thursday.

The contribution marks a major shift for one of the country's most famous business leaders, who's long been known in Democratic circles as a bit of a political tightwad. Though he's given hundreds of thousands to party committees and candidates, Buffett has shunned super-political action committees and other groups that can take unlimited sums. Last cycle, he headlined fundraisers for Obama’s re-election, though he rebuffed solicitations by Priorities USA Action, a super-PAC supporting the president. “I don’t want to see democracy go in that direction,” he said in May 2012 when asked at his company's annual shareholder meeting about his position on giving to outside groups. “You have to take a stand some place.”

Though he supported both Democratic candidates during the 2008 race, Buffett has long been an outspoken Clinton supporter, starting with his backing for her Senate campaign in 2000. Just days after President Barack Obama's re-election, Buffett told CNN that there wasn't anyone better qualified than Clinton for the job in 2016. He also said donating to super-PACs was simply "wrong,"  an opinion that he apparently no longer holds. "Hillary is going to win, yeah," he said at Fortune's Most Powerful Women Summit in October. "I will bet money on it. And I don't do that easily."

Other notable donors to the group, which operates in a similar fashion as a super-PAC, include Irene Hirano, the widow of late Hawaiian Senator Daniel Inouye; former New York Representative Ed Towns; and John Zaccaro, the widower of Geraldine Ferraro, the first woman to run on a major presidential ticket.

Ready for Hillary has no official ties to Clinton. But they've become a campaign-in-waiting for the former secretary of state, amassing a list of 3 million supporters. The organization plans to begin shutting down as soon as Clinton formally announces—if she decides to run, of course. It will make its list of backers available to her campaign, giving Clinton the type of infrastructure any candidate would covet. “We will be at or beyond on Day One of the Clinton campaign, if and when it comes, where we ended up last time,” Jerry Crawford, an Iowa lawyer who's advised Clinton's 2008 presidential campaigns, told reporters at a Ready for Hillary donor summit in New York last month.

In a sign that Ready for Hillary doesn't anticipate closing its doors in the immediate future, organizers took out a $1 million loan—which they plan to repay by March—to expand its direct mail operation, according to the documents. Letters touting its work on behalf of Clinton are being sent to every zip code in the country, according to a strategist involved with the operation, and the investment has doubled their number of donors who give an average of $10 more than those online.

Typically, the mail pieces include a pledge card, photo of Clinton being sworn in as secretary of state, and a solicitation letter from Craig Smith, a long-time Clinton confidant and adviser to Ready for Hillary. "In 2012, Republicans saw that an early, strong organization helped re-elect President Obama. They ignored it then, but I’m sure they won’t make that foolish mistake again," writes Smith. "I believe we owe it to Hillary to show her we’ve got her back."