diff --git a/torchy_baselines/common/base_class.py b/torchy_baselines/common/base_class.py
index 0f20211..7a29847 100644
--- a/torchy_baselines/common/base_class.py
+++ b/torchy_baselines/common/base_class.py
@@ -276,7 +276,7 @@ class BaseRLModel(object):
         :param n_eval_episodes: (int) Number of episode to evaluate the agent
         :return: (BaseRLModel) the trained model
         """
-        pass
+        raise NotImplementedError()
 
     @abstractmethod
     def predict(self, observation, state=None, mask=None, deterministic=False):
@@ -289,7 +289,7 @@ class BaseRLModel(object):
         :param deterministic: (bool) Whether or not to return deterministic actions.
         :return: (np.ndarray, np.ndarray) the model's action and the next state (used in recurrent policies)
         """
-        pass
+        raise NotImplementedError()
 
     def load_parameters(self, load_dict, opt_params):
         """
diff --git a/torchy_baselines/common/vec_env/base_vec_env.py b/torchy_baselines/common/vec_env/base_vec_env.py
index 15a27e1..abc36a8 100644
--- a/torchy_baselines/common/vec_env/base_vec_env.py
+++ b/torchy_baselines/common/vec_env/base_vec_env.py
@@ -58,7 +58,7 @@ class VecEnv(object):
 
         :return: ([int] or [float]) observation
         """
-        pass
+        raise NotImplementedError()
 
     @abstractmethod
     def step_async(self, actions):
@@ -70,7 +70,7 @@ class VecEnv(object):
         You should not call this if a step_async run is
         already pending.
         """
-        pass
+        raise NotImplementedError()
 
     @abstractmethod
     def step_wait(self):
@@ -79,14 +79,14 @@ class VecEnv(object):
 
         :return: ([int] or [float], [float], [bool], dict) observation, reward, done, information
         """
-        pass
+        raise NotImplementedError()
 
     @abstractmethod
     def close(self):
         """
         Clean up the environment's resources.
         """
-        pass
+        raise NotImplementedError()
 
     @abstractmethod
     def get_attr(self, attr_name, indices=None):
@@ -97,7 +97,7 @@ class VecEnv(object):
         :param indices: (list,int) Indices of envs to get attribute from
         :return: (list) List of values of 'attr_name' in all environments
         """
-        pass
+        raise NotImplementedError()
 
     @abstractmethod
     def set_attr(self, attr_name, value, indices=None):
@@ -109,7 +109,7 @@ class VecEnv(object):
         :param indices: (list,int) Indices of envs to assign value
         :return: (NoneType)
         """
-        pass
+        raise NotImplementedError()
 
     @abstractmethod
     def env_method(self, method_name, *method_args, **method_kwargs):
@@ -122,7 +122,7 @@ class VecEnv(object):
         :param method_kwargs: (dict) Any keyword arguments to provide in the call
         :return: (list) List of items returned by the environment's method call
         """
-        pass
+        raise NotImplementedError()
 
     def step(self, actions):
         """