The minimal sub-Planckian axion inflation model accounts for a large scalar-to-tensor ratio via a spiralling trajectory in the field space of a complex field \Phi .
Here we consider how the predictions of the model are modified by Planck scale-suppressed corrections .
In the absence of Planck corrections the model is equivalent to a \phi ^ { 4 / 3 } chaotic inflation model .
Planck corrections become important when the dimensionless coupling \xi of | \Phi| ^ { 2 } to the topological charge density of the strongly-coupled gauge sector F \tilde { F } satisfies \xi \sim 1 .
For values of | \Phi| which allow the Planck corrections to be understood via an expansion in powers of | \Phi| ^ { 2 } / M _ { Pl } ^ { 2 } , we show that their effect is to produce a significant modification of the tensor-to-scalar ratio from its \phi ^ { 4 / 3 } chaotic inflation value without strongly modifying the spectral index .
In addition , to leading order in | \Phi| ^ { 2 } / M _ { Pl } ^ { 2 } , the Planck modifications of n _ { s } and r satisfy a consistency relation , \Delta n _ { s } = - \Delta r / 16 .
Observation of these modifications and their correlation would allow the model to be distinguished from a simple \phi ^ { 4 / 3 } chaotic inflation model and would also provide a signature for the influence of leading-order Planck corrections .