Billionaire Carl Icahn and his investment firm have agreed to pay $2 million to settle with the US Securities and Exchange Commission after an investigation by the regulator.

Icahn is being fined $500,000 and Icahn Enterprises LP will pay $1.5 million related to insufficient disclosure of how IEP units were pledged as collateral against his personal margin loans, according to an SEC statement Monday. The investigation started after a report by short-seller Hindenburg Research sent shares in Icahn’s investment firm tanking.