The agent for Chicago Marathon champion Rita Jeptoo says the Kenyan runner has failed a doping test.

Federico Rosa tells The Associated Press that Jeptoo tested positive for a banned substance in an out-of-competition test in Kenya in September, before she won a second straight title at the Chicago Marathon on Oct. 12.

Rosa declined to name the substance. He said the athlete's "A'' sample tested positive and they were waiting for the backup "B'' sample to be tested.

The 33-year-old Jeptoo has won back-to back titles at the both the Chicago and Boston Marathons and leads the World Marathon Majors series.

The World Marathon Majors postponed Sunday's awards ceremony because of the positive test.