  We present analytical results for higher order corrections to the decay
spectra of inclusive semileptonic heavy hadron weak decays using the heavy
quark expansion (HQE). We compute analytically the spectrum of the leptonic
invariant mass for $B \rightarrow X_c \ell \bar{\nu}$ up to and including terms
of order $1/m_Q^3$ within the HQE at next-to-leading order (NLO) in $\alpha_s$.
The full dependence of the differential rate on the mass of the final-state
quark is taken into account. We discuss the implications of our results for the
precision determination of the CKM matrix element $|V_{cb}|$.
