diff --git a/src/acoustics/discrete_wave/regular/material_scattering_coefficients.jl b/src/acoustics/discrete_wave/regular/material_scattering_coefficients.jl
index a5276ab9..71bf72e5 100644
--- a/src/acoustics/discrete_wave/regular/material_scattering_coefficients.jl
+++ b/src/acoustics/discrete_wave/regular/material_scattering_coefficients.jl
@@ -12,6 +12,7 @@ function material_scattering_coefficients(scat_field::ScatteringCoefficientsFiel
     numdensity = number_density(scat_field.material.species)
 
     particle_radius = maximum(outer_radius.(scat_field.material.species))
+    R = outer_radius(scat_field.material.shape)
 
     function kernel(rθφ)
         x = rθφ2xyz(rθφ)