diff --git a/docs/newforms.txt b/docs/newforms.txt
index b4da35ecd4..88485a7b8c 100644
--- a/docs/newforms.txt
+++ b/docs/newforms.txt
@@ -254,6 +254,24 @@ If your data does *not* validate, your ``Form`` instance will not have a
     ...
     AttributeError: 'ContactForm' object has no attribute 'clean_data'
 
+``clean_data`` will always *only* contain a key for fields defined in the
+``Form``, even if you pass extra data when you define the ``Form``. In this
+example, we pass a bunch of extra fields to the ``ContactForm`` constructor,
+but ``clean_data`` contains only the form's fields::
+
+    >>> data = {'subject': 'hello',
+    ...         'message': 'Hi there',
+    ...         'sender': 'foo@example.com',
+    ...         'cc_myself': True,
+    ...         'extra_field_1': 'foo',
+    ...         'extra_field_2': 'bar',
+    ...         'extra_field_3': 'baz'}
+    >>> f = ContactForm(data)
+    >>> f.is_valid()
+    True
+    >>> f.clean_data # Doesn't contain extra_field_1, etc.
+    {'cc_myself': True, 'message': u'Hi there', 'sender': u'foo@example.com', 'subject': u'hello'}
+
 Behavior of unbound forms
 ~~~~~~~~~~~~~~~~~~~~~~~~~
 
diff --git a/tests/regressiontests/forms/tests.py b/tests/regressiontests/forms/tests.py
index d185f1ceb8..1fc6b3253f 100644
--- a/tests/regressiontests/forms/tests.py
+++ b/tests/regressiontests/forms/tests.py
@@ -1647,6 +1647,17 @@ u'* This field is required.'
 >>> print p['birthday']
 <input type="text" name="birthday" id="id_birthday" />
 
+clean_data will always *only* contain a key for fields defined in the
+Form, even if you pass extra data when you define the Form. In this
+example, we pass a bunch of extra fields to the form constructor,
+but clean_data contains only the form's fields.
+>>> data = {'first_name': u'John', 'last_name': u'Lennon', 'birthday': u'1940-10-9', 'extra1': 'hello', 'extra2': 'hello'}
+>>> p = Person(data)
+>>> p.is_valid()
+True
+>>> p.clean_data
+{'first_name': u'John', 'last_name': u'Lennon', 'birthday': datetime.date(1940, 10, 9)}
+
 "auto_id" tells the Form to add an "id" attribute to each form element.
 If it's a string that contains '%s', Django will use that as a format string
 into which the field's name will be inserted. It will also put a <label> around