diff --git a/moldocker/fitness/threshold.py b/moldocker/fitness/threshold.py
index dc0b8b8..5d85f23 100644
--- a/moldocker/fitness/threshold.py
+++ b/moldocker/fitness/threshold.py
@@ -62,7 +62,7 @@ def get_distances(self, complex):
 
     def normalize(self, value):
         if self.step:
-            return 0 if value > 0 else -1
+            return 0 if value > 0 else -np.inf
         return value