Validators for the Luas has been fixed, after some customers were wrongly being charged peak fares.
Some machines where passengers tag on were running two and half minutes fast.
It means if you tagged on at 6:58 am, you'd be charged the fee for travelling at rush hour.
Tech journalist Jess Kelly broke the story.
She said it was down to what's known as a 'clock drift': "So for those who don't know what clock drift is, sometimes when your computer does a software update, it can be knocked out by a few seconds or a few hours."