Bill Gross has reportedly initiated a short position in U.S. government debt in PIMCO’s Total Return Fund after scaling back the fund’s investments in Treasury bonds.

Gross, who runs the world’s biggest bond fund, is betting on further weakness in Treasurys, accoroding to reports.

PIMCO’s bond guru recently wrote U.S. Treasurys have “little value within the context of a $75 trillion total debt burden.”

Exchange traded funds (ETFs) that invest in Treasury bonds have been falling recently as yields rise, pushing the iShares Barclays 20+ Year Treasury Bond Fund (NYSEArca: TLT) back below $90 a share.

The $6.3 billion ProShares UltraShort 20+ Year Treasury (NYSEArca: TBT) is the largest ETF that bets against Treasury bonds. It shoots for 200% inverse performance on a daily basis.

Other ETFs that profit from rising Treasury yields and lower bond prices include ProShares Short 20+ Year Treasury (NYSEArca: TBF) and Direxion Daily 20 Year Plus Treasury Bear 3x Shares (NYSEArca: TMV).