diff --git a/py_gen/templates/toplevel_init.py b/py_gen/templates/toplevel_init.py
index 72f4c81..b0ee86d 100644
--- a/py_gen/templates/toplevel_init.py
+++ b/py_gen/templates/toplevel_init.py
@@ -56,3 +56,12 @@
     Raised when failing to deserialize an invalid OpenFlow message.
     """
     pass
+
+class Unimplemented(Exception):
+    """
+    Raised when an OpenFlow feature is not yet implemented in PyLoxi.
+    """
+    pass
+
+def unimplemented(msg):
+    raise Unimplemented(msg)