Billionaire George Soros’ investment firm, Soros Fund Management Llc, raised its stake in Tesla Inc.’s convertible bonds due in 2021 by 17.5 million convertible bonds to 37.5 million convertible bonds as of the end of the first quarter, according to a filing with the U.S. Securities and Exchange Commission late Wednesday.

Soros’ increase in the 1.250% convertible bonds follows the firm’s purchase last year of another Tesla convertible bond that came due in March. Soros also previously held some Tesla stock (TSLA), but he sold off his stake in 2017.

A spokesman for Soros did not respond to a request for comment.

Convertibles are hybrid securities, either bonds or preferred stock, that can be exchanged for a predetermined number of common shares. That effectively lets an investor participate in stock-price changes but with the yield and greater security of a fixed-income instrument.

Soros Fund Management also opened a new stake of 200,000 shares in ride-sharing giant Lyft Inc. (LYFT), which went public in late March.

Quarterly disclosures of hedge fund managers’ stock holdings in 13F filings are one of the few public ways of tracking what managers are selling and buying. The disclosures come 45 days after the end of each quarter and may not reflect current positions.