diff --git a/sinergym/utils/wrappers.py b/sinergym/utils/wrappers.py
index 96a5311b9e..e747d9fa96 100644
--- a/sinergym/utils/wrappers.py
+++ b/sinergym/utils/wrappers.py
@@ -405,8 +405,8 @@ def observation(self, obs: np.ndarray) -> np.ndarray:
         new_obs['is_weekend'] = 1.0 if dt.isoweekday() in [6, 7] else 0.0
         new_obs['hour_cos'] = np.cos(2 * np.pi * obs_dict['hour'] / 24)
         new_obs['hour_sin'] = np.sin(2 * np.pi * obs_dict['hour'] / 24)
-        new_obs['month_cos'] = np.cos(2 * np.pi * obs_dict['month'] / 12)
-        new_obs['month_sin'] = np.sin(2 * np.pi * obs_dict['month'] / 12)
+        new_obs['month_cos'] = np.cos(2 * np.pi * (obs_dict['month'] - 1) / 12)
+        new_obs['month_sin'] = np.sin(2 * np.pi * (obs_dict['month'] - 1) / 12)
 
         return np.array(list(new_obs.values()))