NEW YORK (AP) — The agency building the new World Trade Center says a design flaw could add millions of dollars to the cost of the complex’s signature tower.

The Port Authority of New York and New Jersey said Tuesday that the loading dock under One World Trade Center won’t be finished in time for tenants to move their equipment into the 104-story tower. So it’s building five temporary loading bays above ground.

A temporary station that was built for the Port Authority Trans Hudson subway is blocking access to the underground loading area. The station can’t be dismantled to make way for underground freight areas until crews finish the permanent station.

“Several years ago there was a design miss,” Patrick Foye, executive director of the Port Authority, told reporters Tuesday. “Should it have been caught? The answer is, probably.”

The temporary loading bays will add millions to the cost of One World Trade Center, the glass and steel spire previously known as the Freedom Tower. The building is now 90 stories high.

“We and the other concerned stakeholders believe this will be a short-term issue and will not impede completion of the site or tenants moving into the buildings,” Foye said. He spoke after giving a speech to the Association for a Better New York.

The Wall Street Journal on Monday reported that the cost of One World Trade Center has soared to $3.8 billion, $700 million more than the last publicly released estimate in 2008.