diff --git a/src/dials/extensions/radial_profile_spotfinder_threshold_ext.py b/src/dials/extensions/radial_profile_spotfinder_threshold_ext.py
index 3007d82297..5d67765350 100644
--- a/src/dials/extensions/radial_profile_spotfinder_threshold_ext.py
+++ b/src/dials/extensions/radial_profile_spotfinder_threshold_ext.py
@@ -105,7 +105,7 @@ def compute_threshold(
         beam = imageset.get_beam()
 
         # Get 2θ array for the panel or ROI
-        two_theta_array = panel.get_two_theta_array(beam.get_s0())
+        two_theta_array = panel.get_two_theta_array(beam.get_unit_s0())
         if region_of_interest:
             x0, x1, y0, y1 = region_of_interest
             two_theta_array = two_theta_array[y0:y1, x0:x1]