Investors continue to heavily short Tesla Inc.’s (TSLA) high-yield bond, despite having already made a “tidy profit” this year, pushing the cost of opening up new positions betting against the company’s debt to an all-time high, according to IHS Markit.

In a note, Sam Pierson, director of securities finance at the London-based firm, said a lack of profit taking from investors after a successful few months shorting Tesla’s most liquid bond suggests that “they think the credit will continue to deteriorate." The eight-year bond, which matures in 2025, was trading with a yield of 6.58% Monday, the analyst added, representing fears that the electric car maker isn’t capable of delivering on its revised production goals.

The 5.3% coupon issue maturing in 2025 saw short demand trend up last fall, pushing over $280 million in early November, according to IHS Markit evaluated data,” Pierson said in the note. “Coming in to the end of 2017, some short covering coincided with the bonds trading back up to 96 cents on the dollar. This week, IHS Markit shows the mid close price hit 92.5, the lowest level following issuance of the bond in August of last year.”

Demand to short Tesla’s bond has been so high that supply is now said to be wearing thin. Ninety-nine percent of lendable supply for shorting Tesla's high-yield bond has now been used, Pierson said, pushing the cost for new short positions to a record high. (See also: Tesla's $1.5B Bond Offering Picks Up Pace.)

IHS Markit also revealed that Tesla remains the most shorted U.S. equity in dollar terms with a short balance of $9.4 billion.

"With the short demand for Tesla increasing through the recent sell-off — and the short demand for bonds fully utilizing the available supply — it appears short sellers are looking for more downside before they begin to cover," said Pierson. (See also: Stock Market Too Optimistic About Self-Driving Adoption: Morgan Stanley.)