diff --git a/examples/atari/atari_dqn.py b/examples/atari/atari_dqn.py
index f51c7fd..f237c5a 100644
--- a/examples/atari/atari_dqn.py
+++ b/examples/atari/atari_dqn.py
@@ -83,7 +83,7 @@ def get_args() -> argparse.Namespace:
     return parser.parse_args()
 
 
-def test_dqn(args: argparse.Namespace = get_args()) -> None:
+def main(args: argparse.Namespace = get_args()) -> None:
     env, train_envs, test_envs = make_atari_env(
         args.task,
         args.seed,
@@ -260,4 +260,4 @@ def test_dqn(args: argparse.Namespace = get_args()) -> None:
 
 
 if __name__ == "__main__":
-    test_dqn(get_args())
+    main(get_args())
diff --git a/examples/atari/atari_wrapper.py b/examples/atari/atari_wrapper.py
index db1b6b2..a321fb3 100644
--- a/examples/atari/atari_wrapper.py
+++ b/examples/atari/atari_wrapper.py
@@ -39,6 +39,20 @@ def _parse_reset_result(reset_result: tuple) -> tuple[tuple, dict, bool]:
     return reset_result, {}, contains_info
 
 
+def get_space_dtype(obs_space: gym.spaces.Box) -> type[np.floating] | type[np.integer]:
+    obs_space_dtype: type[np.integer] | type[np.floating]
+    if np.issubdtype(obs_space.dtype, np.integer):
+        obs_space_dtype = np.integer
+    elif np.issubdtype(obs_space.dtype, np.floating):
+        obs_space_dtype = np.floating
+    else:
+        raise TypeError(
+            f"Unsupported observation space dtype: {obs_space.dtype}. "
+            f"This might be a bug in tianshou or gymnasium, please report it!",
+        )
+    return obs_space_dtype
+
+
 class NoopResetEnv(gym.Wrapper):
     """Sample initial states by taking random number of no-ops on reset.
 
@@ -199,12 +213,8 @@ class WarpFrame(gym.ObservationWrapper):
         super().__init__(env)
         self.size = 84
         obs_space = env.observation_space
-        obs_space_dtype: type[np.floating[Any]] | type[np.integer[Any]]
-        if np.issubdtype(type(obs_space.dtype), np.integer):
-            obs_space_dtype = np.integer
-        elif np.issubdtype(type(obs_space.dtype), np.floating):
-            obs_space_dtype = np.floating
         assert isinstance(obs_space, gym.spaces.Box)
+        obs_space_dtype = get_space_dtype(obs_space)
         self.observation_space = gym.spaces.Box(
             low=np.min(obs_space.low),
             high=np.max(obs_space.high),
@@ -273,15 +283,11 @@ class FrameStack(gym.Wrapper):
         obs_space_shape = env.observation_space.shape
         assert obs_space_shape is not None
         shape = (n_frames, *obs_space_shape)
-        assert isinstance(env.observation_space, gym.spaces.Box)
-        obs_space_dtype: type[np.floating[Any]] | type[np.integer[Any]]
-        if np.issubdtype(type(obs_space.dtype), np.integer):
-            obs_space_dtype = np.integer
-        elif np.issubdtype(type(obs_space.dtype), np.floating):
-            obs_space_dtype = np.floating
+        assert isinstance(obs_space, gym.spaces.Box)
+        obs_space_dtype = get_space_dtype(obs_space)
         self.observation_space = gym.spaces.Box(
-            low=np.min(env.observation_space.low),
-            high=np.max(env.observation_space.high),
+            low=np.min(obs_space.low),
+            high=np.max(obs_space.high),
             shape=shape,
             dtype=obs_space_dtype,
         )