Jane Fraser’s job as incoming chief executive of Citigroup is to act as a sort of plumber. She needs to fix the U.S. bank’s rusty pipes before they leak again. A New York judge on Tuesday gave her another $500 million incentive to get cracking.

At the heart of the story is a painful example of human error. As Citi (C) was servicing a loan for client Revlon (REV) last year, three people failed to ensure the correct boxes were checked in the bank’s payment software. Instead of paying less than $8 million of interest, the “six eye” team accidentally repaid the roughly $900 million loan. Asset managers accounting for more than half of that refused to give the money back.

Judge Jesse Furman on Tuesday said they don’t have to, essentially because they were owed the money and on balance had no reason to believe the repayment was a mistake. Citi plans to appeal. If not for a 30-year-old precedent involving Banque Worms the U.S. lender might have prevailed, the judge conceded.

But what’s at stake isn’t just the money, equivalent to around 5% of Citi’s earnings last year, but the perception that the bank has yet to get on top of its corrosive habit of carelessness.

Citi’s valuation, based on its price-to-forecast earnings multiple, has lagged its peers for almost a decade, according to Refinitiv data. Sloppiness is one reason. Last October, for instance, the Office of the Comptroller of the Currency fined Citi $400 million for “long-standing failure to establish effective risk management and data governance programs and internal controls.” Roughly three years earlier, the OCC fined Citi for not making improvements it had requested in 2012.

Such recurring problems make it hard to address bigger questions around Citi – like whether its mix of trade finance and credit-card lending makes sense. Fraser, who is replacing Mike Corbat as CEO, is setting up a committee to improve accountability. A new chief administrative officer role, given to former BNY Mellon banker Karen Peetz, also suggests seriousness.

Get it right, and Citi can recover lost ground. Among the eight U.S. companies regulators call systemically important, only scandal-plagued Wells Fargo’s shares have performed worse over a decade. The proof of Fraser’s success will be a higher relative valuation, and the absence of dirty water sloshing around her ankles.