  We study the O(Lambda/mb) corrections to the singly and doubly differential
hadronic invariant mass spectra d\Gamma/dsH and d\Gamma/dsH dq^2 in b -> u
decays, and discuss the implications for the extraction of the CKM matrix
element |Vub|. Using simple models for the subleading shape functions, the
effects of subleading operators are estimated to be at thefew percent level for
experimentally relevant cuts. The subleading corrections proportional to the
leading shape function are larger, but largely cancel in the relation between
the hadronic invariant mass spectrum and the photon spectrum in B -> X_s
\gamma. We also discuss the applicability of the usual prescription of
convoluting the partonic level rate with the leading light-cone wavefunction of
the b quark to subleading order.
