diff --git a/Doc/library/configparser.rst b/Doc/library/configparser.rst
index ec3b022..96c001f 100644
--- a/Doc/library/configparser.rst
+++ b/Doc/library/configparser.rst
@@ -187,8 +187,9 @@
 .. method:: RawConfigParser.add_section(section)
 
    Add a section named *section* to the instance.  If a section by the given name
-   already exists, :exc:`DuplicateSectionError` is raised.
-
+   already exists, :exc:`DuplicateSectionError` is raised. If the name
+   ``DEFAULT`` (or any of it's case-insensitive variants) is passed,
+   :exc:`ValueError` is raised.
 
 .. method:: RawConfigParser.has_section(section)
 
diff --git a/Lib/ConfigParser.py b/Lib/ConfigParser.py
index 131d697..65c6ae2 100644
--- a/Lib/ConfigParser.py
+++ b/Lib/ConfigParser.py
@@ -235,8 +235,12 @@
         """Create a new section in the configuration.
 
         Raise DuplicateSectionError if a section by the specified name
-        already exists.
+        already exists. Raise ValueError if name is DEFAULT or any of it's
+        case-insensitive variants.
         """
+        if section.lower() == "default":
+            raise ValueError, 'Invalid section name: %s' % section
+
         if section in self._sections:
             raise DuplicateSectionError(section)
         self._sections[section] = self._dict()
diff --git a/Lib/test/test_cfgparser.py b/Lib/test/test_cfgparser.py
index c4df741..a8b5d7c 100644
--- a/Lib/test/test_cfgparser.py
+++ b/Lib/test/test_cfgparser.py
@@ -446,6 +446,14 @@
         self.assertRaises(TypeError, cf.set, "sect", "option2", 1.0)
         self.assertRaises(TypeError, cf.set, "sect", "option2", object())
 
+    def test_add_section_default_1(self):
+        cf = self.newconfig()
+        self.assertRaises(ValueError, cf.add_section, "default")
+
+    def test_add_section_default_2(self):
+        cf = self.newconfig()
+        self.assertRaises(ValueError, cf.add_section, "DEFAULT")
+
 class SortedTestCase(RawConfigParserTestCase):
     def newconfig(self, defaults=None):
         self.cf = self.config_class(defaults=defaults, dict_type=SortedDict)
diff --git a/Misc/NEWS b/Misc/NEWS
index a33bf71..89f4c49 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -434,6 +434,9 @@
 Library
 -------
 
+- Issue 1781: ConfigParser now does not let you add the "default" section
+  (ignore-case)
+
 - Removed uses of dict.has_key() from distutils, and uses of
   callable() from copy_reg.py, so the interpreter now starts up
   without warnings when '-3' is given.  More work like this needs to