WASHINGTON (AP) — Long-term U.S. mortgage rates dropped slightly this week.

Mortgage buyer Freddie Mac says the benchmark 30-year, fixed-rate mortgage averaged 3.90 percent, down from 3.91 percent last week. The rate stood at 3.56 percent a year ago and averaged a record low 3.65 percent in 2016.

The 15-year, fixed-rate home loan, popular with homeowners seeking to refinance their mortgages, also blipped lower — to 3.17 percent from 3.18 percent. A year ago, the 15-year rate was 2.83 percent.

The rate on five-year, adjustable-rate mortgages decreased to 3.14 percent from 3.15 percent. It was 2.74 percent a year ago.

Mortgage rates have remained low even though the Federal Reserve has been raising short-term rates: The Fed last week ratcheted rates higher for the third time in six months.

To calculate average mortgage rates, Freddie Mac surveys lenders across the country between Monday and Wednesday each week. The average doesn't include extra fees, known as points, which most borrowers must pay to get the lowest rates. One point equals 1 percent of the loan amount.

The average fees on 30-year, 15-year and five-year adjustable mortgages were unchanged at 0.5 point.