On 21 January 1968 a U.S. B-52 bomber armed with four 1.1-megaton thermonuclear bombs crashed into the ice in Wolstenholme Fjord some ten kilometers southwest of the Thule Airbase in northwest Greenland. The conventional high explosives in the bombs went off on impact, but thanks to the inbuilt safety system no nuclear detonation occurred. However, the crash caused a diplomatic crisis for the U.S. and Danish governments. This article analyzes how the two governments coped with the crisis. The Danish government used the crash as an opportunity to renegotiate the 1951 agreement on the defense of Greenland, which for the previous seventeen years had regulated U.S. military activities on the island. In late May 1968 the two governments agreed to sign a supplementary agreement. The article explains why the Danish government pushed for a major change in the way the nuclear issue was handled in relation to Greenland; it also explains why the U.S. government ultimately agreed to a supplement banning the peacetime introduction of nuclear weapons on Greenland territory, including overflights.