diff --git a/PRL/genF.py b/PRL/genF.py
index a6bc4b9..a45502d 100644
--- a/PRL/genF.py
+++ b/PRL/genF.py
@@ -2,7 +2,7 @@
 import random, math
 from scipy.special import binom
 
-class GenF():
+class GenF(object):
     def __init__(self):
         pass
 
diff --git a/PRL/genP.py b/PRL/genP.py
index be87cf9..da43b01 100644
--- a/PRL/genP.py
+++ b/PRL/genP.py
@@ -1,7 +1,7 @@
 import numpy as np
 import random
 
-class GenP():
+class GenP(object):
     """Abstract class which representes a generic preference generator.
     Every specific generator MUST inherit from this class."""
 
diff --git a/PRL/prl.py b/PRL/prl.py
index 4ec5469..57033f8 100644
--- a/PRL/prl.py
+++ b/PRL/prl.py
@@ -9,7 +9,7 @@
 
 __docformat__ = 'reStructuredText'
 
-class AbstractPRL:
+class AbstractPRL(object):
     """Abstract class which contains the necessary methods for a PRL-based algorithm."""
 
     def get_random_pair(self):