Spectra of two near-IR lines sensitive to hyperfine splitting, comparing the Sun (at disk center) and the K-giant Arcturus, to synthetic ⟨ 3D ⟩ LTE (solid magenta) and ⟨ 3D ⟩ NLTE (solid black) profiles. The spectrum of Arcturus has been shifted downward by 0.2 units. An additional NLTE profile is shown where hyperfine splitting has been neglected (dashed blue). The synthetic profiles were computed assuming A(Al) = 6.43 at 13 123 Å and 6.33 at 16 750 Å for the Sun, and assuming A(Al) = 6.10 and 5.95 for Arcturus.