Stock investors should heed the warning emanating from the bond market, says at least one hedge-fund manager, as the yield curve staged a stunning inversion Friday.

“I think people are going to be surprised where the S&P 500 is trading at the end of the year. We’re going at least for a 40% decline from the S&P’s top,” Otavio Costa, a macro analyst at Crescat Capital.

Costa says the inversion of the yield curve, where short-dated yields rise above their longer-dated peers, signals an ignominious end to a 10-year bull run for the S&P 500 index, which bottomed in March of 2009 but has mounted a record-long rally, by some measures, since that point.

In particular, Costa said the growing number of inversions in yield spreads across Treasury maturities suggested a bear-market for equities was at hand, in the face of a darkening global growth picture.