US President Joe Biden tripped and fell after handing out the last diploma at a graduation ceremony at the US Air Force Academy in Colorado.
The 80-year-old quickly got up on one knee helped by three people and walked back to his seat unassisted.
As Mr Biden was helped up, he pointed behind him, seeming to indicate what he tripped over.
He mingled with other officials afterwards, smiling and giving a "thumbs up" sign.
White House communications director Ben LaBolt said on Twitter that Mr Biden was fine.
"There was a sandbag on stage while he was shaking hands," he explained.
The fall came after Mr Biden delivered a commencement address to a flag-waving audience where he warned graduates they will enter service in an increasingly unstable world, citing challenges from Russia and China.
Mr Biden - the oldest person to hold the Oval Office - is running for re-election in 2024.
Polls show Americans are concerned about anyone over 75 becoming president.
His leading Republican opponent, Donald Trump, turns 77 this month.
Doctors declared him healthy and fit for duty after a physical examination in February, noting he does not drink alcohol or use tobacco and exercises "at least" five times a week.
President Biden fell as he was dismounting his bicycle last June, after catching a foot in a toe clip, but was uninjured.
In November 2020, shortly after winning the election, he broke his foot while playing with a pet dog.
