For students who borrow on the private market to pay for school, the death of a parent can come with an unexpected, added blow, a federal watchdog warns. Even borrowers who have good payment records can face sudden demands for full, early repayment of those loans, and can be forced into default.

Most people who take out loans to pay for school have minimal income or credit history, so if they borrow from banks or other private lenders, they need co-signers — usually parents or other relatives. Borrowing from the federal government, the largest source of student loans, rarely requires a co-signer.

The problem, described in a report released Tuesday by the Consumer Financial Protection Bureau, arises from a little-noticed provision in private loan contracts: If the co-signer dies or files for bankruptcy, the loan holder can demand complete repayment, even if the borrower’s record is spotless. If the loan is not repaid, it is declared to be in default, doing damage to a borrower’s credit record that can take years to repair.

The bureau said that after a co-signer’s death or bankruptcy, some borrowers are placed in default without ever receiving a demand for repayment. The agency did not accuse loan companies of doing anything illegal.