Waymo is issuing a voluntary recall of nearly 3,900 of its autonomous robotaxis in the United States to address a software issue related to freeway work zones. Multiple reports say the problem involves the vehicles entering, and potentially driving at speed through, freeway construction areas that are closed or otherwise blocked. According to filings cited by several outlets, the recall is linked to at least 13 known incidents where Waymo robotaxis drove into construction zones in Phoenix or entered freeway lanes with active construction in the San Francisco area. CBS News and others report that the vehicles in some cases pass ramp-closure signs and enter blocked areas.

Waymo previously paused or restricted parts of its freeway operations in affected cities while improvements are made. The company says it continues to serve riders on surface streets in the markets where it operates. Several outlets report that the recall is expected to be fixed via a free over-the-air software update.

The recall is described as Waymo’s second in just over a month, following an earlier recall tied to flooded roads or standing water.