diff --git a/gym/wrappers/pixel_observation.py b/gym/wrappers/pixel_observation.py
index 6d70d4657e1..9a863c4b1f0 100644
--- a/gym/wrappers/pixel_observation.py
+++ b/gym/wrappers/pixel_observation.py
@@ -7,7 +7,7 @@
 import numpy as np
 
 import gym
-from gym import logger, spaces
+from gym import spaces
 
 STATE_KEY = "state"
 
@@ -95,8 +95,7 @@ def __init__(
 
         default_render_kwargs = {}
         if not env.render_mode:
-            default_render_kwargs = {"mode": "rgb_array_list"}
-            logger.warn(
+            raise AttributeError(
                 "env.render_mode must be specified to use PixelObservationWrapper:"
                 "`gym.make(env_name, render_mode='rgb_array')`."
             )