diff --git a/propti/data_structures.py b/propti/data_structures.py
index 48f0dd9..6eed913 100644
--- a/propti/data_structures.py
+++ b/propti/data_structures.py
@@ -475,6 +475,7 @@ def compute_fitness(self):
         else:
             ds_e_x = ds_e.x
             ds_e_y = ds_e.y
+            ds_e_y2 = None
             if ds_e.y2 is not None:
                 ds_e_y2 = ds_e.y2