Mr Usher said he was unaware of his error as it was a new card
A passenger fined £90 for failing to pay a 90p bus fare, despite having enough money on his Oyster card, has won an appeal.
Tom Usher, 37, from Harlesden, north-west London, was fined and ordered to pay £100 court costs for not validating his card properly on a bendy bus.
But Kingston Crown Court ruled that he had a "reasonable excuse" as he was unaware his fare had not been deducted.
Mr Usher was "overjoyed", but said "it shouldn't have come to this".
He had £1.60 on his Oyster card when challenged by an inspector on a bendy bus in December last year.
Mr Usher said he was unaware of his error as it was a new card, but Transport for London (TfL) successfully prosecuted him in Wimbledon Magistrates Court.
His sentence was quashed on Friday when the court noted that bus passengers were not warned to check for a green light and a beep when touching their cards onto the reader.
Outside court Mr Usher said: "If something's wrong you have got to complain about it. If everyone starts complaining then maybe things will change."
A TfL spokesman said it was "disappointed" but accepted the decision.
"This case did not call into question our prosecutions policy or the need to prosecute fare evasion on London's buses, which costs taxpayers more than £30m a year," he added.
TfL estimated that each prosecution for fare evasion cost about £270, but it would not reveal how much it cost to prosecute Mr Usher.