A record $1 trillion of junk debt will mature by 2021, leaving high-risk companies to hunt for new cash at a time when markets are likely to be less welcoming, according to Moody's Investors Service.

Speculative-grade companies have $1.06 trillion of debt maturing between 2017 and 2021, with the bulk of it, $933 billion, coming due after 2019, Moody's said in a report Wednesday. New issuance is likely to rise in the second half of this year to start addressing those maturities, analysts led by Tiina Siilaberg wrote.

Debt markets aren't prepared to absorb the maturities, according to Moody's. Demand for collateralized loan obligations, which bundle leveraged corporate loans into securities, has fallen from its 2014 peak, and credit ratings for both bank loans and high-yield bonds have deteriorated, according to the report.