One of Nick Willis's rivals for the Olympic 1500m title will contest the final after originally being excluded from the competition for not trying in a 800m heat.
Algerian runner Taoufik Makhloufi won his 1500m semi-final in three minutes 42.24 seconds on Sunday night, surprisingly beating Kenyan Olympic and world champion Asbel Kiprop.
He lined up in heat five of the 800m on Monday, but started very slowly before giving up after half a lap and stepping off the track.
The race referee ruled that the 24-year-old African 800m champion was guilty of "failure to compete honestly with bona fide effort" but the Algerian federation said he had a knee problem that organisers knew about.
After assessing evidence of a Games medical officer, the disqualification was revoked and Makhloufi can compete in Tuesday's 1500m final.
"After reviewing evidence provided by a LOCOG (Games organisers) medical officer, the disqualification of athlete 1008 (Taoufik Makhloufi) from further participation in the athletics competition of the 2012 Olympic Games has been revoked by the IAAF technical delegates. Consequently, Mr Makhloufi is able to compete," a statement said.
Willis qualified third fastest for the final.