diff --git a/weboob/tools/backend.py b/weboob/tools/backend.py
index 580615ce..0ea7c971 100644
--- a/weboob/tools/backend.py
+++ b/weboob/tools/backend.py
@@ -215,6 +215,9 @@ class BaseBackend(object):
         def not_loaded(v):
             return (v is NotLoaded or isinstance(value, CapBaseObject) and not value.__iscomplete__())
 
+        if isinstance(fields, basestring):
+            fields = (fields,)
+
         missing_fields = []
         if fields is None or '*' in fields:
             if isinstance(obj, CapBaseObject):