The man from Saarland was due a tax rebate of €400, but received instead a bank-account-boosting payment of €85,000, daily newspaper Die Welt reported.
And because the tax authorities did not contact him to ask for the money back for eight years, a court ruled on Wednesday, it was too late and the man could keep the money.
The Federal Tax Court said the five-year limit on claims for restitution from the tax office applied in this case.
The civil servants who had failed to contact the man for such a long time after the overpayment could not do anything more to get the money back.
The man did not contact the tax office about the overpayment, but kept quiet – and can now spend the money.