diff --git a/Demo/classes/bitvec.py b/Demo/classes/bitvec.py
index 2894a56ae76..495a83727a1 100755
--- a/Demo/classes/bitvec.py
+++ b/Demo/classes/bitvec.py
@@ -6,7 +6,8 @@
 
 import sys; rprt = sys.stderr.write #for debugging
 
-error = 'bitvec.error'
+class error(Exception):
+    pass
 
 
 def _check_value(value):