diff --git a/django/contrib/flatpages/models.py b/django/contrib/flatpages/models.py
index 896bfa3eac..42bb3adf23 100644
--- a/django/contrib/flatpages/models.py
+++ b/django/contrib/flatpages/models.py
@@ -11,10 +11,12 @@ class FlatPage(models.Model):
     url = models.CharField(_('URL'), max_length=100, db_index=True)
     title = models.CharField(_('title'), max_length=200)
     content = models.TextField(_('content'), blank=True)
-    enable_comments = models.BooleanField(_('enable comments'))
+    enable_comments = models.BooleanField(_('enable comments'), default=False)
     template_name = models.CharField(_('template name'), max_length=70, blank=True,
         help_text=_("Example: 'flatpages/contact_page.html'. If this isn't provided, the system will use 'flatpages/default.html'."))
-    registration_required = models.BooleanField(_('registration required'), help_text=_("If this is checked, only logged-in users will be able to view the page."))
+    registration_required = models.BooleanField(_('registration required'),
+        help_text=_("If this is checked, only logged-in users will be able to view the page."),
+        default=False)
     sites = models.ManyToManyField(Site)
 
     class Meta:
diff --git a/django/db/models/fields/__init__.py b/django/db/models/fields/__init__.py
index 1f0ce5e4ed..142b33f6a7 100644
--- a/django/db/models/fields/__init__.py
+++ b/django/db/models/fields/__init__.py
@@ -620,8 +620,6 @@ class BooleanField(Field):
 
     def __init__(self, *args, **kwargs):
         kwargs['blank'] = True
-        if 'default' not in kwargs and not kwargs.get('null'):
-            kwargs['default'] = False
         Field.__init__(self, *args, **kwargs)
 
     def get_internal_type(self):
diff --git a/docs/ref/models/fields.txt b/docs/ref/models/fields.txt
index 421de74c62..f22436e5fe 100644
--- a/docs/ref/models/fields.txt
+++ b/docs/ref/models/fields.txt
@@ -377,6 +377,10 @@ The default form widget for this field is a
 If you need to accept :attr:`~Field.null` values then use
 :class:`NullBooleanField` instead.
 
+.. versionchanged:: 1.6
+    The default value of ``BooleanField`` was changed from ``False`` to
+    ``None`` when :attr:`Field.default` isn't defined.
+
 ``CharField``
 -------------
 
diff --git a/docs/releases/1.6.txt b/docs/releases/1.6.txt
index db9c597490..f3d12cac38 100644
--- a/docs/releases/1.6.txt
+++ b/docs/releases/1.6.txt
@@ -292,6 +292,20 @@ should either restore Django's defaults at the end of each request, force an
 appropriate value at the beginning of each request, or disable persistent
 connections.
 
+``BooleanField`` no longer defaults to ``False``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+When a :class:`~django.db.models.BooleanField` doesn't have an explicit
+:attr:`~django.db.models.Field.default`, the implicit default value is
+``None``. In previous version of Django, it was ``False``, but that didn't
+represent accurantely the lack of a value.
+
+Code that relies on the default value being ``False`` may raise an exception
+when saving new model instances to the database, because ``None`` isn't an
+acceptable value for a :class:`~django.db.models.BooleanField`. You should
+either specify ``default=False`` explicitly on the field definition, or ensure
+the field is set to ``True`` or ``False`` before saving the object.
+
 Translations and comments in templates
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
diff --git a/tests/model_fields/tests.py b/tests/model_fields/tests.py
index eaf84773e3..d3b1e4b868 100644
--- a/tests/model_fields/tests.py
+++ b/tests/model_fields/tests.py
@@ -6,7 +6,7 @@ from decimal import Decimal
 from django import test
 from django import forms
 from django.core.exceptions import ValidationError
-from django.db import models
+from django.db import models, IntegrityError
 from django.db.models.fields.files import FieldFile
 from django.utils import six
 from django.utils import unittest
@@ -265,6 +265,18 @@ class BooleanFieldTests(unittest.TestCase):
         self.assertEqual(mc.bf.bfield, False)
         self.assertEqual(mc.nbf.nbfield, False)
 
+    def test_null_default(self):
+        """
+        Check that a BooleanField defaults to None -- which isn't
+        a valid value (#15124).
+        """
+        b = BooleanModel()
+        self.assertIsNone(b.bfield)
+        with self.assertRaises(IntegrityError):
+            b.save()
+        nb = NullBooleanModel()
+        self.assertIsNone(nb.nbfield)
+        nb.save()           # no error
 
 class ChoicesTests(test.TestCase):
     def test_choices_and_field_display(self):
diff --git a/tests/model_inheritance_regress/tests.py b/tests/model_inheritance_regress/tests.py
index 98216dbc84..c2c9337485 100644
--- a/tests/model_inheritance_regress/tests.py
+++ b/tests/model_inheritance_regress/tests.py
@@ -181,11 +181,11 @@ class ModelInheritanceTest(TestCase):
         """
         Regression test for #6755
         """
-        r = Restaurant(serves_pizza=False)
+        r = Restaurant(serves_pizza=False, serves_hot_dogs=False)
         r.save()
         self.assertEqual(r.id, r.place_ptr_id)
         orig_id = r.id
-        r = Restaurant(place_ptr_id=orig_id, serves_pizza=True)
+        r = Restaurant(place_ptr_id=orig_id, serves_pizza=True, serves_hot_dogs=False)
         r.save()
         self.assertEqual(r.id, orig_id)
         self.assertEqual(r.id, r.place_ptr_id)