When qualifying closed at 6 p.m. on Wednesday May 28, the field had only been filled to 28 cars. Duke Dinsmore was the final qualifier, completing his run amidst some scoring confusion by the officials, just as the time had run out. Race officials initially stressed that Wednesday would be the final day available to qualify. However, a day later, they re-opened qualifying for one hour late on Thursday May 29 in an effort to fill the field. Mel Hansen and Emil Andres were the only two cars to complete attempts, and after approval by the other entries, were added to the grid to bring the field to 30 cars.