Chief Justice John Roberts, who first administered the oath to Obama on Tuesday on the steps of the US Capitol, administered it again to the president on Wednesday in front of reporters and a few members of the president's staff.
"We believe that the oath of office was administered effectively and that the president was sworn in appropriately yesterday," Press Secretary Robert Gibbs told a hastily gathered group of journalists, quoting a statement from White House counsel Greg Craig.
"But the oath appears in the Constitution itself and, out of an abundance of caution, because there was one word out of sequence, Chief Justice John Roberts will administer the oath a second time."
Then Gibbs ushered reporters into the Map Room, where Obama was waiting, smiling, along with the chief justice. The president visited with journalists and then stood next to Roberts and took the oath again.
During the ceremony on the steps of the Capitol on Tuesday Roberts accidentally switched the word order when he administered the oath, saying "I will execute the office of president to the United States faithfully," instead of, "I will faithfully execute the office of president of the United States."
Obama, who briefly interrupted the chief justice by starting the oath before Roberts finished reciting the first part, then repeated back the line as Roberts had said it.
On Wednesday, Obama joked with reporters that he wanted to do it again for fun.
"We decided, you know, that it was so much fun!" he said.
Then Roberts asked him if he was ready to take the oath.
"I am. We're going to do it very slowly," Obama said.
Obama raised his right hand, Roberts administered the oath in the right order, and Obama repeated it correctly.
"Congratulations again," the chief justice said after they were finished.
"Thank you sir," Obama replied as staff members applauded.