E-scooter hire company Lime has warned about a fault that can lead to riders being flung off scooters at high speed.
The fault, which has caused injuries, strikes most often when scooters hit bumps while going full speed downhill.
The bug meant the scooter suddenly applied "excessive braking", said Lime.
A software update had "resulted in a material reduction of occurrences", it said, but riders should check the brakes before starting a journey until all Lime scooters had been updated.
Bumps and bruises
In its advisory note, Lime said its statistics suggested that the sudden braking bug had affected less than 0.0045% of all the rides taken on its scooters.
But, it added, even this small number had meant some riders had been hurt, mainly by "bumps and bruises" caused when they fell off.
"Data shows scooters are a safe form of transportation, comparable to or safer than bicycles," it said.
To stay safe, e-scooter users should also wear a helmet, respect local road laws and be cautious.
Lime scooters are available in more than 100 cities and are used for more than one million rides per month.
The warning comes soon after a study by the Consumer Reports watchdog showed there had been more than 1,500 scooter-related accidents in the US since 2017.
At least three riders are known to have died in accidents involving the scooters.
The most recent death was of Irish exchange student Mark Sands, who died in Austin, Texas , on 2 February, after colliding with a Uber car.
After the study was published, William Wallace, a senior policy analyst at Consumer Reports, said: "Right now, a stunning number of e-scooter users are getting seriously hurt, including with head injuries.
"Consumers, scooter companies, cities, helmet-makers, and safety regulators must work together now to improve the safety of these products."