A number of the machines were running two minutes and 30 seconds fast
The Luas operator Transdev says clocks on its validator machines have been fixed, after it emerged some customers were wrongly being charged peak fares.
A number of the machines where passengers tag-on were found to be running two minutes and 30 seconds fast.
It means validating your journey at 6.58am would see you incur the fare for travelling during peak rush hour.
Trandev say the validators are set by its AFCS, or Automatic Fare Collection System and CSS, Central Support System.
It says: "It is possible that PC clock drift can occur due to hardware or software faults or device restarts.
"This issue has been checked by our technicians and a fix will be implemented shortly."
It adds: "The fare you pay is determined by tag-on time rather than tag-off time.
"If a device time was incorrectly set you could pay peak rate (€2.50 max) rather than off-peak rate (€2.45 max) during the period the device was away from real time.
"The inverse is also true, the device would charge off-peak rates at the other end of the time window."