The 30-year bond has produced a total return of 5.5% this year.

“But because of the mechanics of bond investing, it wouldn’t take much of a rise in interest rates to take those gains away,” according to MarketBeat. “That’s because, with yields this low, prices tend to swing wildly with relatively small changes in yields — meaning rates don’t have to increase much to generate sizable bond-price declines. In other words, be careful out there if you’re betting on long-term U.S. Treasurys.”

The iShares Barclays 20+ Year Treasury Bond (NYSEArca: TLT) is up about 6% the past month.

iShares Barclays 20+ Year Treasury Bond