  In this letter we discuss a regularization scheme for the integration of
generic on-shell forms. The basic idea is to extend the three-particle
amplitudes to the space of unphysical helicities keeping the dimension of the
related coupling constant fixed, and construct on-shell forms out of them. We
briefly discuss the analytic structure of the extended on-shell diagrams, both
at tree level and one loop. Furthermore, we propose an integration contour
which, applied to the relevant on-shell forms, allows to extract the
four-particle amplitudes in Lorentz signature at one loop. With this contour at
hand, we explicitly apply our procedure to this case obtaining the IR
divergences as poles in the deformation parameter space, as well as the correct
functional form for the finite term. This procedure provides a natural
regularization for generic on-shell diagrams.
