At the 2004 Summer Olympics in Athens, Alleyne maintained his program by qualifying for two swimming events. He cleared FINA B-standard entry times of 51.89 (100 m freestyle) and 1:53.19 (200 m freestyle) from the Pan American Games in Santo Domingo, Dominican Republic. In the 200 m freestyle, Alleyne challenged seven other swimmers on the third heat, including fellow two-time Olympians Joshua Ilika Brenner of Mexico and Giancarlo Zolezzi of Chile. He edged out Algeria's Mahrez Mebarek to take a third spot and thirty-fourth overall by 0.11 of a second in 1:52.89. In his second event, 100 m freestyle, Alleyne placed forty-eighth overall on the morning's preliminaries. Swimming in heat three, Alleyne matched his entry time of 51.89 to save a fifth spot over Zolezzi's compatriot Max Schnettler by 0.02 of a second.