diff --git a/mushroom_rl/core/array_backend.py b/mushroom_rl/core/array_backend.py
index 706357c4..bd0a8c48 100644
--- a/mushroom_rl/core/array_backend.py
+++ b/mushroom_rl/core/array_backend.py
@@ -11,6 +11,10 @@ class ArrayBackend(object):
     def get_backend_name():
         raise NotImplementedError
 
+    @staticmethod
+    def get_backend_serialization():
+        raise NotImplementedError
+
     @staticmethod
     def get_array_backend(backend_name):
         assert type(backend_name) == str, f"Backend has to be string, not {type(backend_name).__name__}."
@@ -174,6 +178,10 @@ class NumpyBackend(ArrayBackend):
     def get_backend_name():
         return 'numpy'
 
+    @staticmethod
+    def get_backend_serialization():
+        return 'numpy'
+
     @staticmethod
     def to_numpy(array):
         return array
@@ -303,6 +311,10 @@ class TorchBackend(ArrayBackend):
     def get_backend_name():
         return 'torch'
 
+    @staticmethod
+    def get_backend_serialization():
+        return 'torch'
+
     @staticmethod
     def to_numpy(array):
         return None if array is None else array.detach().cpu().numpy()
@@ -438,6 +450,10 @@ class ListBackend(ArrayBackend):
     def get_backend_name():
         return 'list'
 
+    @staticmethod
+    def get_backend_serialization():
+        return 'numpy'
+
     @staticmethod
     def to_numpy(array):
         return np.array(array)
diff --git a/mushroom_rl/rl_utils/preprocessors.py b/mushroom_rl/rl_utils/preprocessors.py
index 921b2e41..30721080 100644
--- a/mushroom_rl/rl_utils/preprocessors.py
+++ b/mushroom_rl/rl_utils/preprocessors.py
@@ -1,5 +1,3 @@
-import numpy as np
-
 from mushroom_rl.core import Serializable, ArrayBackend
 from mushroom_rl.rl_utils.running_stats import RunningStandardization
 
@@ -122,9 +120,9 @@ def __init__(self, mdp_info, backend, clip_obs=10., alpha=1e-32):
         self._add_save_attr(
             _array_backend='pickle',
             _run_norm_obs='primitive',
-            _obs_mask='numpy',
-            _obs_mean='numpy',
-            _obs_delta='numpy'
+            _obs_mask=self._array_backend.get_backend_serialization(),
+            _obs_mean=self._array_backend.get_backend_serialization(),
+            _obs_delta=self._array_backend.get_backend_serialization()
         )
 
     def __call__(self, obs):