Barack Obama has been sworn in as US president for the second time in two days, because one word was given out of order during Tuesday's ceremony.
The Chief Justice of the US Supreme Court, John Roberts, administered the oath again at the White House.
The decision to repeat the oath was taken out of an abundance of caution, an official said.
But Mr Obama joked: "We decided it was so much fun...." before adding: "We're going to do it very slowly."
In contrast to the first oath-taking, Mr Obama did not swear on a Bible and his wife Michelle was not at his side.
And instead of an audience of millions, only a few close aides saw the second attempt, with even journalists excluded from the Map Room of the White House.
Tuesday's stumble went largely unnoticed at the time.
In the oath, as set out in the US Constitution, the new incumbent swears to "faithfully execute the office of president of the United States".
But as Chief Justice Roberts read out the oath for Mr Obama to repeat, he moved the word "faithfully" to the end of the phrase.
Mr Obama, apparently noticing the error, hesitated. Mr Roberts repeated the phrase correctly, but Mr Obama went with the incorrect formula.
"We believe the oath of office was administered effectively and that the president was sworn in appropriately," said White House counsel Greg Craig.
"Out of the abundance of caution, because there was one word out of sequence, Chief Justice John Roberts will administer the oath a second time."
Two other presidents, Calvin Coolidge and Chester Arthur, have had to repeat the oath because of similar problems.And Chief Justice William Taft introduced a new word into the oath when he swore in President Herbert Hoover in 1929, promising to "preserve, maintain and defend the Constitution", instead of "preserve, protect and defend".