A doping ban handed to former world 800 metres champion Tatyana Andrianova of Russia was overturned on Thursday because the authorities failed to re-test her sample in time.
Andrianova won bronze at the 2005 world championships in Finland and her sample was deemed clean.
When it was re-tested last year it showed traces of the banned steroid stanozolol and she was given a two-year suspension by the Russian Athletics Federation (ARAF).
Adrianova's results from 2005-07, including her bronze medal, were also annulled.
She appealed against the ban and the Court of Arbitration for Sport (CAS) ruled in her favour because the limit for re-testing samples is eight years.
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"As the eight-year statute of limitations had expired prior to January 1 2015, the 10-year statute of limitations provided under the new 2015 anti-doping rules cannot apply," CAS said in a statement.
Russian athletics is embroiled in a massive international doping crisis and the country is currently banned from the sport.
The IAAF governing body will decide next month whether enough progress has been made in reforming Russia's anti-doping operation to allow it back into competition in time to take part at the Olympic Games in Rio de Janeiro in August.
