We investigate two-photon detachment of an inner 1s electron from the 1s22s2 ground state of Li- using R-matrix Floquet theory. This detachment rate shows a noticeable structure due to shape resonances just above the lowest three doubly excited thresholds of Li. Two-photon detachment of one 1s electron is about twice as likely as two-photon detachment of (at least) one 2s electron. Two-photon detachment of one 1s electron may be observable experimentally through the detection of electrons with kinetic energies between 45 and 65 eV.