Wavelengths for emission lines arising from 3s23p5-3s3p6 and 3s23p5-3s23p43d transitions in Ni XII have been measured in extreme ultraviolet spectra of the Joint European Torus(JET) tokamak. The 3s23p5 2P1/2-3s23p4(3P)3d 2D3/2 line is found to lie at 152.90 ± 0.02 A, a significant improvement over the previous experimental determination of 152.95 ± 0.5 A. This new wavelength is in good agreement with a solar identification at 152.84 ± 0.06 A, confirming the presence of this line in the solar spectrum. The Ni XII feature at 152.15 A may be a result only of the 3s23p5 2P3/2-3s23p4(3P)3d 2D5/2 transition, rather than a blend of this line with 3s23p5 2P3/2-3s23p (3P)3d 2P1/2, as previously suggested. Unidentified emission lines at 295.32 and 317.61 A in solar flare spectra from the Skylab mission are tentatively identified as the 3s23p5 2P3/2-3s3p6 2S1/2 and 3s23p5 2P1/2-3s3p6 2S1/2 transitions in Ni XII, which have laboratory wavelengths of 295.33 and 317.50 A, respectively. Additional support for these identifications is provided by the line intensity ratio for the solar features, which shows good agreement between theory and observation.