Index: django/db/models/fields/__init__.py
===================================================================
--- django/db/models/fields/__init__.py (revision 6363)
+++ django/db/models/fields/__init__.py (working copy)
@@ -1,3 +1,4 @@
+import copy
 import datetime
 import os
 import time
@@ -398,6 +399,11 @@
         "Returns the value of this field in the given model instance."
         return getattr(obj, self.attname)
 
+    def __deepcopy__(self,memo):
+        result = copy.copy(self)
+        memo[id(self)] = result
+        return result
+
 class AutoField(Field):
     empty_strings_allowed = False
     def __init__(self, *args, **kwargs):