diff --git a/src/pyg4ometry/mcnp/Surfaces.py b/src/pyg4ometry/mcnp/Surfaces.py
index f41e8c77b..4c2264b4f 100644
--- a/src/pyg4ometry/mcnp/Surfaces.py
+++ b/src/pyg4ometry/mcnp/Surfaces.py
@@ -313,3 +313,4 @@ def __init__(self, z, t_sqr, sign):
     def __repr__(self):
         return f"KZ: {self.z} {self.t_sqr} {self.sign}"
 
+