diff --git a/common/lib/capa/capa/xqueue_interface.py b/common/lib/capa/capa/xqueue_interface.py
index 75db0870c0..2847968a89 100644
--- a/common/lib/capa/capa/xqueue_interface.py
+++ b/common/lib/capa/capa/xqueue_interface.py
@@ -55,7 +55,7 @@ def parse_xreply(xreply):
     return (return_code, content)
 
 
-class XQueueInterface:
+class XQueueInterface(object):
     '''
     Interface to the external grading system
     '''