  In a previous article we have shown the existence of a new independent R^4
term, at one loop, in the type IIA and heterotic effective actions, after
reduction to four dimensions, besides the usual square of the Bel-Robinson
tensor. It had been shown that such a term could not be directly
supersymmetrized, but we showed that was possible after coupling to a scalar
chiral multiplet. In this article we study the extended (N=8)
supersymmetrization of this term, where no other coupling can be taken. We show
that such supersymmetrization cannot be achieved at the linearized level. This
is in conflict with the theory one gets after toroidal compactification of type
II superstrings being N=8 supersymmetric. We interpret this result in face of
the recent claim that perturbative supergravity cannot be decoupled from string
theory in d>=4, and N=8, d=4 supergravity is in the swampland.
