diff --git a/examples/units/evans_test.py b/examples/units/evans_test.py
index 72acfb4bf6ca..c5fe9696d2fb 100644
--- a/examples/units/evans_test.py
+++ b/examples/units/evans_test.py
@@ -27,7 +27,7 @@ def value(self, unit):
         return self._val / unit
 
 
-class FooConverter(object):
+class FooConverter(units.ConversionInterface):
     @staticmethod
     def axisinfo(unit, axis):
         'return the Foo AxisInfo'