diff --git a/django/forms/fields.py b/django/forms/fields.py
index ab746e4971..9070963607 100644
--- a/django/forms/fields.py
+++ b/django/forms/fields.py
@@ -753,13 +753,15 @@ class NullBooleanField(BooleanField):
     def to_python(self, value):
         """
         Explicitly checks for the string 'True' and 'False', which is what a
-        hidden field will submit for True and False, and for '1' and '0', which
-        is what a RadioField will submit. Unlike the Booleanfield we need to
-        explicitly check for True, because we are not using the bool() function
+        hidden field will submit for True and False, for 'true' and 'false',
+        which are likely to be returned by JavaScript serializations of forms,
+        and for '1' and '0', which is what a RadioField will submit. Unlike
+        the Booleanfield we need to explicitly check for True, because we are
+        not using the bool() function
         """
-        if value in (True, 'True', '1'):
+        if value in (True, 'True', 'true', '1'):
             return True
-        elif value in (False, 'False', '0'):
+        elif value in (False, 'False', 'false', '0'):
             return False
         else:
             return None
diff --git a/tests/forms_tests/tests/test_fields.py b/tests/forms_tests/tests/test_fields.py
index 1a6286451e..2482fe0682 100644
--- a/tests/forms_tests/tests/test_fields.py
+++ b/tests/forms_tests/tests/test_fields.py
@@ -1000,6 +1000,8 @@ class FieldsTests(SimpleTestCase):
         self.assertEqual(None, f.clean('2'))
         self.assertEqual(None, f.clean('3'))
         self.assertEqual(None, f.clean('hello'))
+        self.assertEqual(True, f.clean('true'))
+        self.assertEqual(False, f.clean('false'))
 
     def test_nullbooleanfield_2(self):
         # Make sure that the internal value is preserved if using HiddenInput (#7753)