diff --git a/weboob/capabilities/base.py b/weboob/capabilities/base.py
index 972e80c1..667fcb1c 100644
--- a/weboob/capabilities/base.py
+++ b/weboob/capabilities/base.py
@@ -29,6 +29,9 @@ class NotAvailableMeta(type):
     def __unicode__(self):
         return u'Not available'
 
+    def __nonzero__(self):
+        return False
+
 
 class NotAvailable(object):
     __metaclass__ = NotAvailableMeta
@@ -41,6 +44,9 @@ class NotLoadedMeta(type):
     def __unicode__(self):
         return u'Not loaded'
 
+    def __nonzero__(self):
+        return False
+
 
 class NotLoaded(object):
     __metaclass__ = NotLoadedMeta