diff --git a/deep_rl/utils/normalizer.py b/deep_rl/utils/normalizer.py
index 95ffd47..fa183c6 100644
--- a/deep_rl/utils/normalizer.py
+++ b/deep_rl/utils/normalizer.py
@@ -5,7 +5,7 @@
 #######################################################################
 import numpy as np
 
-class BaseNormalizer:
+class BaseNormalizer(object):
     def __init__(self, read_only=False):
         self.read_only = read_only