Self-driving car company Waymo issued its first-ever recall on Tuesday after an incident in Phoenix.

The company said two of its autonomous vehicles collided with a pickup truck in Phoenix. The incidents, which took place last December, occurred when two Waymo vehicles collided with a tow truck that was improperly towing another vehicle. According to Waymo, the incident occurred due to a software error that failed to properly predict the movement of vehicles being towed. New software was installed in all of its vehicles between late December 2023 and January 2024. Approximately 444 vehicles were impacted. 

“After developing, rigorously testing, and validating a fix, on Dec. 20, 2023, we began deploying a software update to our fleet to address this issue,” the company said in a blog post addressing the issue.

After reporting the issue and discussing with the National Highway Traffic Safety Administration, Waymo leaders decided a voluntary recall was appropriate. 

Rideshare service using the vehicles was not hindered at any time due to the error.