Average 30-year fixed mortgage rates in the U.S. were flat in the latest week, according to mortgage-finance company Freddie Mac (FMCC).

Overall, mortgage rates were little changed during the period, in which economic reports were light, Freddie Mac Chief Economist Frank Nothaft noted in a statement Thursday. Of the few economic reports, the Institute for Supply Management's manufacturing index for August came in stronger than expected and marked its highest reading since March 2011.

For the week ended Thursday, the 30-year fixed-rate mortgage averaged 4.1%, unchanged from a week earlier and down from 4.57% a year earlier. Rates on 15-year fixed-rate mortgages averaged 3.24%, compared with 3.25% the previous week and 3.59% a year earlier.

Five-year Treasury-indexed hybrid adjustable-rate mortgages, or ARMs, on average, were at 2.97%, unchanged from the previous week and down from 3.28% a year earlier. One-year Treasury-indexed ARM rates on average were 2.4%, compared with 2.39% the previous week and 2.71% a year earlier.

Write to Tess Stynes at tess.stynes@wsj.com

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