After an elevator mishap caused the Washington Monument to close early Wednesday afternoon, the 555-foot obelisk reopened to the public on Thursday.

The monument closed at 3:30 p.m. Wednesday after the elevator stopped working at the 500-foot level, the National Mall National Park Service said in a tweet.

While no one was in the elevator when the incident happened, about 40 guests at the top of the monument had to evacuate by walking down hundreds of stairs. The visitors included a group of Georgia high school students who were visiting the monument during a field trip, the Gwinnett Daily Post reported.

“Technicians have determined that a faulty sensor is the source of the problem with the Washington Monument elevator,” the National Mall NPS tweeted. The sensor gave errant readings that caused the elevator to shut down, the agency continued.

Technicians fixed the issue Thursday morning and the monument was reopened at 10:30 a.m., an NPS representative tells DCist.

The Washington Monument opened in September after three years of repairs, which included construction on a new security facility and renovations to its elevator system.

Since then, the monument has already been experiencing technical difficulties, including a loss of power that caused the monument to close for a few hours on November 16.