diff --git a/focus_utils.py b/focus_utils.py
index 8ee82fb..5cc51ad 100644
--- a/focus_utils.py
+++ b/focus_utils.py
@@ -123,7 +123,8 @@ def fitFocusCurve(
         if coeffs[2] < 0:
             coeffs[2] = 0
 
-        scale = np.abs(np.nanmedian(flux_rad - nr_res(focus_value)))
+        nr_model = nr_res(np.asarray(focus_value))
+        scale = np.abs(np.nanmedian(flux_rad - nr_model))
         # robust fitting
         res = least_squares(
             polyModelResid,