Fannie Mae has said it will tighten lending standards on adjustable-rate mortgages and "interest-only" loans that helped fuel the housing bubble and have led to a disproportionate share of losses for the mortgage-finance giant.

The changes, which will take effect in September, will require lenders to qualify borrowers based on whether or not they can afford potentially higher payments once adjustable-rate loans reset, and will require much more stringent criteria for interest-only borrowers.

Wall Street Journal