diff --git a/bin/osv/fields.py b/bin/osv/fields.py
index e03f76b3541..5a56130985e 100644
--- a/bin/osv/fields.py
+++ b/bin/osv/fields.py
@@ -478,6 +478,9 @@ class many2many(_column):
     def __init__(self, obj, rel, id1, id2, string='unknown', limit=None, **args):
         _column.__init__(self, string=string, **args)
         self._obj = obj
+        if '.' in rel:
+            raise Exception(_('The second argument of the many2many field %s must be a SQL table !'\
+                'You used %s, which is not a valid SQL table name.')% (string,rel))
         self._rel = rel
         self._id1 = id1
         self._id2 = id2