The founder of Pakistan’s nuclear weapons program says it took six years for his country to weaponize highly enriched uranium.

Abdul Qadeer Khan gave an interview to a local television station late last month in which he said Pakistan successfully enriched uranium using centrifuges for the first time in 1978. He said it took six years from that point to develop a nuclear bomb.

This may mean that North Korea will also take at least several years to develop a highly enriched uranium bomb. Pyongyang has recently claimed success in enriching uranium.

Former senior Pakistani officials and experts in the U.S. say the Pakistani nuclear scientist helped North Korea attain the knowledge and equipment necessary for uranium enrichment.