The tallest residential tower in San Francisco, and the city’s third tallest overall, has sunk 16 inches since it’s opening in 2008, according to SFGate.

Designed by Handel Architects, the Millennium Tower is one of the highest-profile buildings in the city with units selling as high as $12 million for a penthouse, one of which was owned by venture capitalist Thomas Perkins until his death earlier this year. Other notable residents include San Francisco Giants outfielder Hunter Pence and former 49ers quarterback Joe Montana.

Currently the Transbay Transit Center, a transit station and neighborhood development project, is under construction on an adjacent site. Its first phase is due to be completed in late 2017, but a study of the site conducted by Arup in 2010 found that the tower had already sunk ten inches. Initial predictions for the tower suggested that it would only sink six inches over its lifetime.

Of added concern is the fact that the tower is not settling evenly, and now has a tilt of two inches. Professor Greg Deierlein of the John A. Blume Earthquake Engineering Center at Stanford University told SFGate that these figures were “significant…and of concern,” but not yet a threat to safety. However, the imbalance can lead to expensive maintenance costs down the road due to cracking walls and other structural issues.

The Transbay Transit Center and the building’s developer, Millennium Partners, have each placed blame for the tilt on the other. P.J. Johnson, a spokesperson for Millennium Partners, told SFGate that the nearby construction on the Transit Center caused the problem, suggesting that adequate measures were not taken to protect the tower during the excavation. Representatives of the Transit Center, on the other hand, have suggested that Millennium engineers cut costs and failed to anchor the building into the bedrock. The building also uses concrete rather than steel, and is therefore much heavier.

It’s unclear what steps developers will take to combat the issue, but it will likely involve expensive and complicated repairs.