When Monsanto agreed to pay regulators $80 million Tuesday for accounting missteps, the giant agribusiness’s chief executive also chipped in: He voluntarily agreed to return his bonus for the years the problems allegedly occurred.

Hugh Grant, who has served as Monsanto’s CEO for more than a decade, will return more $3,165,852 in cash bonuses and stock awards to the company. Carl Casale, the company’s former chief financial officer, will give back $728,843. It is the first time in memory that senior executives voluntarily agreed to return their bonuses in such a case.

Neither was accused of wrongdoing by the Securities and Exchange Commission, making the voluntary relinquishment of their bonuses even more unusual.

Monsanto was accused of booking millions of revenue after launching a rebate program for one of its popular herbicide products, Roundup, but not properly accounting for the cost of the promotion. By 2009, according to the SEC, Monsanto’s Roundup was losing ground to cheaper competitors. It began to offer retailers or distributors rebates in order to encourage them to carry the herbicide despite its higher prices. The program helped boost sales, but when reporting its profits to shareholders, Monsanto did not reflect the cost of the effort, the SEC says.

“As a result of the improper accounting, Monsanto met consensus earnings-per-share analyst estimates for fiscal year 2009,” according to the SEC filing on the case.

“This type of conduct … is the latest page from a well-worn playbook of accounting misstatements,” SEC Chair Mary Jo White said in a statement.

Monsanto did not admit wrongdoing. “The company is pleased to put this matter behind it and remains focused on building value for its shareowners,” the company said in a statement.

Grant and Casale were not totally selfless by agreeing to return their bonuses. Under Sarbanes Oxley, the accounting rules adopted in 2002 in the wake of Enron and Worldcom,  the SEC could have gone after that money anyway, though it is less likely to do so when the executive has not been accused of wrongdoing.

The SEC has been more active on the issue over the last few years, said Carol Bowie, executive director at Institutional Shareholder Services. “But it is still pretty rare,” she said.

The vast majority – 87 percent – of companies on the Standard & Poors 500 have corporate clawback provisions that could be used to force an executive to forfeit their bonus in some circumstances, according to ISS  QuickScore.  But it is unclear how often those provisions are used, said Bowie. “There is very little disclosure to date,” she said.

Shareholders have been pushing to have these clawback provisions expanded to include not just executives caught committing misdeeds, but their supervisors, and to urge companies to disclose when clawbacks are used, said Bowie.

Grant, 57, should be able to recoup his losses quickly. Monsanto increased his base pay 6.5 percent last year to $1.6 million. He also received a $1.9 million bonus and is eligible for nearly $10 million in “long-term incentives.”

This story has been updated.