A guarantee mortgage is a loan that is guaranteed by a third party, such as a government institution. It has been common practice, for example, for a party associated with the credit line borrower to execute a guarantee mortgage to secure the credit line obligations of the primary obligor.

The guaranty mortgage does not secure the borrower's revolving obligation, only a sum certain that could be owed the lender, which could be equal to the maximum amount outstanding at any one time under the credit line.

Although generally accepted practice, the Tax Commission has informally advised that it may end this manner of avoidance by taxing the guarantee mortgage as amounts are re-advanced under the borrower's primary obligation. Guarantee mortgages will then need to be expressly non-revolving and secure the last amounts repaid under the borrower's loan.