diff --git a/product/ERP5Form/ProxyField.py b/product/ERP5Form/ProxyField.py
index 8462c8e8a496ebb7d2cfeddbe76875079875bd8f..425e8e76f7737796d7caedc09268dadf2e372fec 100644
--- a/product/ERP5Form/ProxyField.py
+++ b/product/ERP5Form/ProxyField.py
@@ -513,7 +513,10 @@ class ProxyField(ZMIField):
     """
       Return a callable expression
     """
-    tales_expr = self.get_tales_expression(id)
+    try:
+      tales_expr = self.get_tales_expression(id)
+    except ValueError:
+      return None
     if tales_expr:
       return TALESValue(tales_expr)
 
diff --git a/product/ERP5Form/tests/testFields.py b/product/ERP5Form/tests/testFields.py
index 41ca902b4dc95969a5db583f1ad3cfeeecd27ef1..d9ed0c9533d11788a13d1d487cd89d08adf977bf 100644
--- a/product/ERP5Form/tests/testFields.py
+++ b/product/ERP5Form/tests/testFields.py
@@ -130,6 +130,8 @@ class TestProxyField(unittest.TestCase):
                       'my_title', 'Not Title', 'ProxyField')
     proxy_field = self.container.Base_view.my_title
     self.assertEquals(None, proxy_field.getTemplateField())
+    self.assertEquals(None, proxy_field.get_value('enable'))
+    self.assertEquals(None, proxy_field.get_value('default'))
 
     proxy_field.manage_edit_xmlrpc(dict(form_id='Base_viewProxyFieldLibrary',
                                         field_id='my_title',))