Google's self-driving cars have been involved in fender benders in the past, but have always been deemed the innocent party. But it turns out, the Web giant's autonomous vehicles aren't actually perfect.

Google on Feb. 23 filed a report with the California Department of Motor Vehicles revealing that one of its autonomous vehicles—a self-driving Lexus—recently struck the side of a passing bus. The incident occurred Feb. 14 on El Camino Real, a six-lane highway in Google's hometown of Mountain View, Calif., after the vehicle, driving in autonomous mode, pulled toward a right-hand curb to prepare for a right turn.

After pulling towards the right, the vehicle "detected sandbags near a storm drain blocking its path, so it needed to come to a stop," according to an advance copy of Google's February self-driving monthly report, provided to PCMag on Monday. "After waiting for some other vehicles to pass, our vehicle, still in autonomous mode, began angling back toward the center of the lane at around 2 mph — and made contact with the side of a passing bus traveling at 15 mph.  Our car had detected the approaching bus, but predicted that it would yield to us because we were ahead of it."

Google said its test driver, who had been watching the bus in the mirror, also expected it to slow or stop.

"We can imagine the bus driver assumed we were going to stay put," Google wrote. "Unfortunately, all these assumptions led us to the same spot in the lane at the same time. This type of misunderstanding happens between human drivers on the road every day."

Google's car suffered some "body damage" to the left front fender, the left front wheel, and one of its driver's side sensors, but no injuries were reported.

Google said it "clearly" bears "some responsibility" for the crash — because if its car hadn't moved, there wouldn't have been a collision. But the Web giant isn't taking all the blame.

"Our test driver believed the bus was going to slow or stop to allow us to merge into the traffic, and that there would be sufficient space to do that," the company said.

Google said it has reviewed the incident, and thousands of variations on it, in its simulator and made refinements to its self-driving car software to prevent a similar incident from happening again.

"From now on, our cars will more deeply understand that buses (and other large vehicles) are less likely to yield to us than other types of vehicles, and we hope to handle situations like this more gracefully in the future," Google wrote. 

This article originally appeared on PCMag.com.