FORTUNE — A U.K. financial regulator has fined Barclays BCS $43.8 million after it accused a former trader at the bank of improperly influencing gold prices.

The British bank will be fined £26 million ($43.8 million) for failures that allowed trader Daniel James Plunkett to exploit the weaknesses in Barclays’ systems and controls to seek to influence the price of gold, which allowed the firm to “profit at a customer’s expense,” according to a news release.

The fine was handed down by the Financial Conduct Authority. Separately, Plunkett was fined £95,600, or about $161,000.

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“A firm’s lack of controls and a trader’s disregard for a customer’s interests have allowed the financial services industry’s reputation to be sullied again,” said Tracey McDermott, the FCA’s director of enforcement and financial crime.

“Plunkett has paid a heavy price for putting his own interests above the integrity of the market and Barclays’ customer,” she said. “Traders who might be tempted to exploit their clients for a quick buck should be in no doubt – such behavior will cost you your reputation and your livelihood.”