diff --git a/bin/osv/fields.py b/bin/osv/fields.py
index 851f5d4d432..c6186b9a052 100644
--- a/bin/osv/fields.py
+++ b/bin/osv/fields.py
@@ -64,6 +64,10 @@ class _column(object):
     _symbol_get = None
 
     def __init__(self, string='unknown', required=False, readonly=False, domain=None, context=None, states=None, priority=0, change_default=False, size=None, ondelete="set null", translate=False, select=False, **args):
+        if domain is None:
+            domain = []
+        if context is None:
+            context = {}
         self.states = states or {}
         self.string = string
         self.readonly = readonly
@@ -74,8 +78,8 @@ class _column(object):
         self.change_default = change_default
         self.ondelete = ondelete
         self.translate = translate
-        self._domain = domain or []
-        self._context = context or {}
+        self._domain = domain
+        self._context = context
         self.write = False
         self.read = False
         self.view_load = 0
diff --git a/bin/osv/orm.py b/bin/osv/orm.py
index 4d63bdd805a..c5a47d1201f 100644
--- a/bin/osv/orm.py
+++ b/bin/osv/orm.py
@@ -131,6 +131,10 @@ class browse_record(object):
         table : the object (inherited from orm)
         context : dictionary with an optional context
         '''
+        if fields_process is None:
+            domain = {}
+        if context is None:
+            context = {}
         self._list_class = list_class or browse_record_list
         self._cr = cr
         self._uid = uid
@@ -139,8 +143,8 @@ class browse_record(object):
         self._table_name = self._table._name
         self.__logger = logging.getLogger(
             'osv.browse_record.' + self._table_name)
-        self._context = context or {}
-        self._fields_process = fields_process or {}
+        self._context = context
+        self._fields_process = fields_process
 
         cache.setdefault(table._name, {})
         self._data = cache[table._name]