Google self-drive car has been pulled over by police in Mountain View, California, for driving too slowly.
No action was taken but it does raise questions about whether the cars, in their current form, are too cautious.
In a post on Google+, the net giant joked: "Bet humans don't get pulled over for that too often."
An accident report recently filed by the California Department of Motor Vehicles described a Google automated car as "over-cautious".
In a blogpost about this week's incident, the Mountain View police department said an officer "noticed traffic backing up behind a slow-moving car in the eastbound lane".
"The officer stopped the car... to learn more about how it was choosing speeds along certain roadways and to educate the operators about impeding traffic," it added.
The car was travelling at 24mph in a 35mph zone.
In its own post about the incident, Google said: "We've capped the speed of our prototype vehicles at 25mph for safety reasons. We want them to feel friendly and approachable, rather than zooming scarily through neighbourhood streets."