diff --git a/n3fit/src/n3fit/layers/preprocessing.py b/n3fit/src/n3fit/layers/preprocessing.py
index 4b85fbde3b..5acf3435be 100644
--- a/n3fit/src/n3fit/layers/preprocessing.py
+++ b/n3fit/src/n3fit/layers/preprocessing.py
@@ -37,7 +37,7 @@ class Preprocessing(MetaLayer):
 
     def __init__(
         self,
-        replica_seeds: Optional[List[int]],
+        replica_seeds: List[int],
         flav_info: Optional[list] = None,
         large_x: bool = True,
         **kwargs,