diff --git a/openerp/fields.py b/openerp/fields.py
index 748576c6cfd..5f7255c7e24 100644
--- a/openerp/fields.py
+++ b/openerp/fields.py
@@ -1223,6 +1223,10 @@ class Selection(Field):
             selection = api.expected(api.model, selection)
         super(Selection, self).__init__(selection=selection, string=string, **kwargs)
 
+    def _setup(self, env):
+        super(Selection, self)._setup(env)
+        assert self.selection is not None, "Field %s without selection" % self
+
     def _setup_related(self, env):
         super(Selection, self)._setup_related(env)
         # selection must be computed on related field
diff --git a/openerp/models.py b/openerp/models.py
index 5badd8dd905..5f596cdd5f9 100644
--- a/openerp/models.py
+++ b/openerp/models.py
@@ -239,7 +239,7 @@ class MetaModel(api.Meta):
         # transform columns into new-style fields (enables field inheritance)
         for name, column in self._columns.iteritems():
             if name in self.__dict__:
-                _logger.warning("Field %r erasing an existing value", name)
+                _logger.warning("In class %s, field %r overriding an existing value", self, name)
             setattr(self, name, column.to_field())
 
 
@@ -461,16 +461,14 @@ class BaseModel(object):
     @classmethod
     def _add_field(cls, name, field):
         """ Add the given `field` under the given `name` in the class """
-        field.set_class_name(cls, name)
-
-        # add field in _fields (for reflection)
+        # add field as an attribute and in cls._fields (for reflection)
+        if not isinstance(getattr(cls, name, field), Field):
+            _logger.warning("In model %r, field %r overriding existing value", cls._name, name)
+        setattr(cls, name, field)
         cls._fields[name] = field
 
-        # add field as an attribute, unless another kind of value already exists
-        if isinstance(getattr(cls, name, field), Field):
-            setattr(cls, name, field)
-        else:
-            _logger.warning("In model %r, member %r is not a field", cls._name, name)
+        # basic setup of field
+        field.set_class_name(cls, name)
 
         if field.store:
             cls._columns[name] = field.to_column()