Olympic champion LaShawn Merritt was cleared to defend his 400-meter title in London next year after the American won his appeal Thursday against an IOC rule banning doping offenders from the games.

The Court of Arbitration for Sport annulled the International Olympic Committee rule that bars any athlete who has received a doping suspension of more than six months from competing in the next summer or winter games.

The three-man CAS panel said the rule, adopted in 2008, was "invalid and unenforceable" because it amounted to a second sanction and did not comply with the World Anti-Doping Agency code. It said the rule amounted to a "disciplinary sanction" rather than a matter of eligibility.

Merritt, the American 400-meter gold medalist in Beijing, had been ineligible under the IOC rule to compete in London even though he completed his doping ban this year after testing positive for a banned substance found in a male-enhancement product.