diff --git a/scopesim/optics/optical_element.py b/scopesim/optics/optical_element.py
index 82b29ba7..a9a98e61 100644
--- a/scopesim/optics/optical_element.py
+++ b/scopesim/optics/optical_element.py
@@ -132,12 +132,13 @@ def get_z_order_effects(self, z_level: int, z_max: int = None):
                     f"{z_max=} < {z_level=}.")
         else:
             z_max = z_min + 100  # range doesn't include final element -> 100
+        z_range = range(z_min, z_max)
 
         for eff in self.effects:
             if not eff.include or "z_order" not in eff.meta:
                 continue
 
-            if z_order_in_range(eff.meta["z_order"], range(z_min, z_max)):
+            if z_order_in_range(eff.meta["z_order"], z_range):
                 yield eff
 
     @property