Loss of constraint triaxiality with plastic deformation severely limits the applicability of small specimens to fracture toughness measurement in the ductile-brittle transition region. In earlier work, the authors developed a framework for correcting cleavage fracture toughness data for constraint loss. The present article presents a simple constraint correction equation that increases the measuring capacity of fracture toughness specimens, that is, it is now possible to measure higher valid toughness values with small specimens than was previously possible. At present, the constraint correction can be applied only to the low-to-mid transition region, but ongoing work is aimed at extending the approach to the upper transition region, where cleavage is preceded by stable tearing. Current work is also addressing three-dimensional effects.