Waymo is recalling nearly 4,000 robotaxis after regulators found that some vehicles entered closed freeway construction zones during multiple incidents.

The recall covers 3,871 vehicles using Waymo’s 5th Generation Automated Driving System and follows 13 reported cases, including several in the San Francisco Bay Area.

The National Highway Traffic Safety Administration said the software may fail to properly recognize certain construction-zone closures, allowing vehicles to continue at normal speeds.

Waymo began investigating the issue in April and has already restricted freeway driving while developing a software fix, Fox Business has reported.

The company says the recall is voluntary and part of ongoing efforts to improve safety in its driverless fleet.