U.S. President Donald Trump wished Prime Minister Shinzo Abe, his golf buddy and close ally, a “very happy birthday” on Monday, at the start of a formal signing ceremony for his country’s recently reached trade deal with Japan.

But there was just one problem — Abe’s birthday is on Sept. 21.

Rather, Monday was the birthday of another leader often associated with Trump: Russian President Vladimir Putin.

“I want to start by wishing my very good friend, Prime Minister Abe of Japan, a very happy birthday. He’s 39 years old today,” Trump said to laughter, mispronouncing, as he often does, the Japanese leader’s name as “abby.”

Abe turned 65 late last month, and it was clear that Trump’s reference to his age was a joke. But it was not clear why he had wished Abe a happy birthday on Monday of all days, though the mercurial U.S. leader is infamous for his often jarring syntax, verbal flubs and even blatant lies.

The White House did not immediately respond to a request for comment.

Putin, who turned 67 on Monday, spent the weekend in southern Siberia’s mountains.

The U.S. intelligence community has repeatedly said that the Russian government — on the explicit orders of Putin — interfered in the 2016 U.S. presidential election with the goal of harming the campaign of Hillary Clinton, boosting the candidacy of Trump and increasing political and social discord in the United States.

Trump has denied this was the case.

When it comes to Abe, who is widely said to have the closest personal ties with Trump among all foreign leaders, the American president has had a fair number of instances where he appeared to embarrass the prime minister or leave him dumbfounded.

These have included Trump’s revelation that he had, in private, pushed Abe to nominate him for the Nobel Peace Prize, and also referred to the prime minister as “president” of Japan.

Ultimately, though, the pair’s relationship has survived dire straits more menacing than mere gaffes and unfortunate disclosures, including the bilateral trade deal, which was viewed by some observers as the price Abe paid for keeping in Trump’s good graces.

Indeed, speaking Monday about Abe, the U.S. leader had nothing but praise, calling him “a very special man.”

“He’s a great gentleman and we have had tremendous success,” Trump said.