U.S. mortgage rates plummeted last week, as investors continue to fear slower international economic growth.

According to Freddie Mac, the average rate on a 30-year fixed-rate mortgage (FRM) loan dropped to 4.06%, down from 4.28% the week before and the largest weekly decrease since June 2009. Rates on 15-year FRMs also fell, averaging 3.57%, down from 3.71% the previous week. Lower rates will be a welcome gift to potential homebuyers this spring.