diff --git a/database_cleanup/models/purge_properties.py b/database_cleanup/models/purge_properties.py
index 9f62762f0..61d7dd9f7 100644
--- a/database_cleanup/models/purge_properties.py
+++ b/database_cleanup/models/purge_properties.py
@@ -20,6 +20,7 @@ class CleanupPurgeLineProperty(models.TransientModel):
         (REASON_DUPLICATE, 'Duplicated property'),
         (REASON_DEFAULT, 'Same value as default'),
         (REASON_DEFAULT_FALSE, 'Empty default property'),
+        (REASON_UNKNOWN_MODEL, 'Unknown model'),
     ])
 
     @api.multi