Building on the definition of the double-copy extended gravitational field as a convolution of two vectors, we construct the action for N = 0 supergravity as a double copy up to cubic order. We discuss the connection of our findings to tensionless strings and show the existence of gauge fixings that mix the two spin-one sectors and lead to an alternative, and simpler, version of the Lagrangian. Whereas gauge invariance alone would not suffice to uniquely fix the couplings of the double-copy action, all ambiguities disappear upon imposing a left-right Lorentz symmetry ruling contraction of indices among double-copy fields. Such a twofold Lorentz symmetry, however, conflicts with the perturbative reconstruction of spacetime geometry.