diff --git a/zippydoc/block_markup.py b/zippydoc/block_markup.py
index 3d1187d..cec6fd0 100644
--- a/zippydoc/block_markup.py
+++ b/zippydoc/block_markup.py
@@ -1,7 +1,7 @@
 import re
 from value import Value
 
-class TreeLevel:
+class TreeLevel(object):
 	def __init__(self, indentation, data):
 		self.elements = []
 		self.indentation = indentation
diff --git a/zippydoc/document.py b/zippydoc/document.py
index bbfd741..dc1d5be 100644
--- a/zippydoc/document.py
+++ b/zippydoc/document.py
@@ -1,7 +1,7 @@
 import re
 import block_markup
 
-class Document():
+class Document(object):
 	def __init__(self, data):
 		self.data = data
 		self._parse()
diff --git a/zippydoc/transformation_ruleset.py b/zippydoc/transformation_ruleset.py
index d1b1c37..13a5c2d 100644
--- a/zippydoc/transformation_ruleset.py
+++ b/zippydoc/transformation_ruleset.py
@@ -1,4 +1,4 @@
-class TransformationRuleset():
+class TransformationRuleset(object):
 	def transform_children(self, text):
 		pass