The talk-show host closed his segment with Trump by asking if he could do one silly thing with him since he could be president the next time he appears on the show.
'I'm not liking the sound of this,' Trump said before Fallon asked if he could mess his hair up.
The audience roared as the Republican nominee pondered the bizarre request but he ultimately agreed.
'The answer is yes, but... I hope the people of New Hampshire... will understand,' Trump said, noting he would be there later tonight and did not want his coiffure out of place. But Fallon certainly sent Trump's locks flying out of control in every direction.
And while Trump is known for being sensitive about his hair, he smiled throughout the hilarious ordeal.
Afterwards, he tried to push his hair back in place, but it largely resisted.