Pilots who want to be among the first to fly the F-35 will need to pack on some pounds to even be allowed in the cockpit.

Following some worrisome ejection seat tests, the military has decided to restrict pilots weighing less than 136 pounds from flying the fighter jet. Maj. Gen. Jeffrey Harrigian said this policy will stay in effect until the program can make seat ejection more safe for lightweight pilots.

“The bottom line is, they have to get into the realm where the seat allows that weight of a pilot less than 136 pounds [to] safely eject out of the airplane,” Harrigian said. “They found some areas that particularly at slower speeds they were concerned about, so that drove the restriction that we have right now.”

During August tests, researchers realized that the ejection seat over-rotated for lighter pilots. They became worried that when the parachute deploys, a lighter pilot will not be in the best position to eject.