diff --git a/gprMax/utilities.py b/gprMax/utilities.py
index a6a1a28c..5c9c42cb 100644
--- a/gprMax/utilities.py
+++ b/gprMax/utilities.py
@@ -21,7 +21,7 @@ import decimal as d
 from pyfiglet import Figlet
 
 
-class ListStream:
+class ListStream(object):
     """A list can be streamed into. Required when temporarily redirecting stdio to capture output from users Python code blocks."""
     
     def __init__(self):