foo.diff

diff --git a/django/core/exceptions.py b/django/core/exceptions.py
index 62c4d0b..418eaab 100644
--- a/django/core/exceptions.py
+++ b/django/core/exceptions.py
@@ -3,6 +3,7 @@ Global Django exception and warning classes.
 """
 from functools import reduce
 import operator
+import copy
 
 from django.utils.encoding import force_text
 
@@ -85,7 +86,15 @@ class ValidationError(Exception):
         of ValidationError with its `error_list` or `error_dict` attribute set.
         """
         if isinstance(message, ValidationError):
-            self.__dict__.update(message.__dict__)
+            if hasattr(message, 'error_dict'):
+                self.error_dict = copy.copy(message.error_dict)
+            elif not hasattr(message, 'message'):
+                self.error_list = copy.copy(message.error_list)
+            else:
+                self.message = message.message
+                self.code = message.code
+                self.params = copy.copy(message.params)
+                self.error_list = [self]
 
         elif isinstance(message, dict):
             self.error_dict = {}
diff --git a/tests/forms_tests/tests/test_forms.py b/tests/forms_tests/tests/test_forms.py
index 7f30b0e..faccda1 100644
--- a/tests/forms_tests/tests/test_forms.py
+++ b/tests/forms_tests/tests/test_forms.py
@@ -693,6 +693,7 @@ class FormsTestCase(TestCase):
                     self.add_error('password1', 'Forbidden value 2.')
                 if self.cleaned_data.get('password2') == 'FORBIDDEN_VALUE2':
                     self.add_error('password2', 'Forbidden value 2.')
+                    raise ValidationError("I'm a non field error.")
 
                 return self.cleaned_data
 
@@ -729,7 +730,7 @@ class FormsTestCase(TestCase):
         self.assertEqual(f.errors['password2'], ['Forbidden value.'])
 
         f = UserRegistration({'username': 'adrian', 'password1': 'FORBIDDEN_VALUE2', 'password2': 'FORBIDDEN_VALUE2'}, auto_id=False)
-        self.assertEqual(f.errors['__all__'], ['Forbidden value 2.'])
+        self.assertEqual(f.errors['__all__'], ['Forbidden value 2.', "I'm a non field error."])
         self.assertEqual(f.errors['password1'], ['Forbidden value 2.'])
         self.assertEqual(f.errors['password2'], ['Forbidden value 2.'])