The cracks were described as thin, and were found on the canopy longeron sill between the front and back seats of the popular, but aging, fighter. The F-16D is primarily used for training purposes nowadays, although that doesn't make this problem any less troubling.
According to Stars and Stripes, the USAF's F-16 Program Office said in a statement that it's developing a temporary fix alongside Lockheed Martin. That would allow the planes to fly in a limited capacity until a more permanent fix is sorted out.
The USAF currently maintains a fleet of nearly 1,000 F-16s.