A recent failure analysis of nickel-copper K-500 fasteners that failed in air associated the rate-dependent, intergranular fracture mode with the presence of grain boundary carbon films and precipitates. The exact mechanism of rate-dependent fracture in that instance was unknown. However, mechanisms such as hydrogen-assisted cracking and creep are known to be consistent with the circumstances of that failure. To determine whether hydrogen-assisted cracking could be affected by grain boundary carbon amount and morphology, the present study examines the influence of intergranular carbon precipitates and various levels of hydrogen on the fracture behavior of nickel-copper Alloy K-500. Dichotomous results indicate that hydrogen-assisted intergranular fracture associated with carbon precipitates may occur in this alloy at lower bulk hydrogen levels than previously reported, yet carbon precipitates may inhibit susceptibility to hydrogen embrittlement under cathodic charging conditions. The latter result is discussed with respect to a possible competitive interaction between hydrogen-assisted and carbon-precipitate-induced intergranular fracture modes.