Abstract We use globular cluster data from the Resolved Stellar Populations Early Release Science (ERS) program to validate the flux calibration for the Near Infrared Camera (NIRCam) on the James Webb Space Telescope. We find a significant flux offset between the eight short wavelength detectors, ranging from 1% to 23% (∼0.01–0.2 mag) that affects all NIRCam imaging observations. We deliver improved zero-points for the ERS filters and show that alternate zero-points derived by the community also improve the calibration significantly. We also find that the detector offsets appear to be time variable by up to at least 0.1 mag.