Researchers have found a flaw in the technical setup of an experiment that startled the science world last year by appearing to show particles traveling faster than light.

The problem may have affected measurements that clocked subatomic neutrino particles breaking what Einstein considered the ultimate speed barrier.

Two separate issues were identified with the GPS system that was used to time the arrival of neutrinos at an underground lab in Italy, according to James Gillies, spokesman for the European Organization for Nuclear Research, or CERN.

One could have caused the speed to be overestimated, the other could have caused it to be underestimated, he said Wednesday.

“The bottom line is that we will not know until more measurements are done later this year,” Gillies said.