diff --git a/django/contrib/flatpages/forms.py b/django/contrib/flatpages/forms.py
index b2811ff618..3916c85a89 100644
--- a/django/contrib/flatpages/forms.py
+++ b/django/contrib/flatpages/forms.py
@@ -16,11 +16,13 @@ class FlatpageForm(forms.ModelForm):
         url = self.cleaned_data.get('url', None)
         sites = self.cleaned_data.get('sites', None)
 
-        flatpages_with_same_url = FlatPage.objects.filter(url=url)
+        same_url = FlatPage.objects.filter(url=url)
+        if self.instance.pk:
+            same_url = same_url.exclude(pk=self.instance.pk)
 
-        if flatpages_with_same_url.filter(sites__in=sites).exists():
+        if same_url.filter(sites__in=sites).exists():
             for site in sites:
-                if flatpages_with_same_url.filter(sites=site).exists():
+                if same_url.filter(sites=site).exists():
                     raise forms.ValidationError(
                         _('Flatpage with url %s already exists for site %s'
                           % (url, site)))
diff --git a/django/contrib/flatpages/tests/forms.py b/django/contrib/flatpages/tests/forms.py
index 83437ba733..7f617d52a5 100644
--- a/django/contrib/flatpages/tests/forms.py
+++ b/django/contrib/flatpages/tests/forms.py
@@ -1,5 +1,6 @@
 from django.conf import settings
 from django.contrib.flatpages.forms import FlatpageForm
+from django.contrib.flatpages.models import FlatPage
 from django.test import TestCase
 
 class FlatpageAdminFormTests(TestCase):
@@ -35,3 +36,23 @@ class FlatpageAdminFormTests(TestCase):
         self.assertEqual(
             f.errors,
             {'__all__': [u'Flatpage with url /myflatpage1 already exists for site example.com']})
+
+    def test_flatpage_admin_form_edit(self):
+        """
+        Existing flatpages can be edited in the admin form without triggering
+        the url-uniqueness validation.
+
+        """
+        existing = FlatPage.objects.create(
+            url="/myflatpage1", title="Some page", content="The content")
+        existing.sites.add(settings.SITE_ID)
+
+        data = dict(url='/myflatpage1', **self.form_data)
+
+        f = FlatpageForm(data=data, instance=existing)
+
+        self.assertTrue(f.is_valid(), f.errors)
+
+        updated = f.save()
+
+        self.assertEqual(updated.title, "A test page")