diff --git a/mushroom_rl/features/basis/polynomial.py b/mushroom_rl/features/basis/polynomial.py
index 1b1fe75d..3483dce4 100644
--- a/mushroom_rl/features/basis/polynomial.py
+++ b/mushroom_rl/features/basis/polynomial.py
@@ -37,6 +37,8 @@ def __init__(self, dimensions=None, degrees=None, low=None, high=None):
         if low is not None:
             self._mean = (low + high) / 2
             self._delta = (high - low) / 2
+        else:
+            self._mean = None
 
     def __call__(self, x):
 
@@ -53,6 +55,7 @@ def __call__(self, x):
     def _normalize(self, x):
         if self._mean is not None:
             return (x - self._mean) / self._delta
+        return x
 
     def __str__(self):
         if self._deg is None:
diff --git a/mushroom_rl/policy/noise_policy.py b/mushroom_rl/policy/noise_policy.py
index 1a95bfb2..317d4eab 100644
--- a/mushroom_rl/policy/noise_policy.py
+++ b/mushroom_rl/policy/noise_policy.py
@@ -114,7 +114,6 @@ def __init__(self, mu, sigma, low, high):
         self._add_save_attr(
             _approximator='mushroom',
             _predict_params='pickle',
-            _inv_sigma='numpy',
             _sigma='numpy',
             _low='numpy',
             _high='numpy'