According to NY Daily News, Watson flew into New York's John F. Kennedy International Airport (JFK) over the Christmas holiday and was questioned by agents at passport control who mistook her for an unaccompanied minor.
On Dec. 22, Watson recounted the incident to her 4.9 million Twitter followers.
According to AirSafe.com, the maximum age for an unaccompanied minor is 12 for most airlines. However, teens under the age of 18 can sometimes opt to use the unaccompanied minor service, though it is typically not required.
It is unclear whether officers at JFK believed Watson to be under 12 or 18.
More than 18,000 people have since retweeted Watson's comment, with many fans expressing their astonishment at the agents' mistake.
A few minutes after her first tweet, the petite starlet followed up by stating that her age has been underestimated before.
Still, despite her exasperation, many of Watson's fans noted on Twitter that being mistaken for someone young is hardly a bad thing.
For more on Watson, click through this slideshow to see her style over the years: