diff -r 9d4e0445cdce Lib/enum.py
--- a/Lib/enum.py	Thu Oct 03 14:39:39 2013 -0600
+++ b/Lib/enum.py	Thu Oct 03 23:00:36 2013 +0100
@@ -15,14 +15,16 @@
 
 def _is_dunder(name):
     """Returns True if a __dunder__ name, False otherwise."""
-    return (name[:2] == name[-2:] == '__' and
+    return (len(name) > 4 and
+            name[:2] == name[-2:] == '__' and
             name[2:3] != '_' and
             name[-3:-2] != '_')
 
 
 def _is_sunder(name):
     """Returns True if a _sunder_ name, False otherwise."""
-    return (name[0] == name[-1] == '_' and
+    return (len(name) > 2 and
+            name[0] == name[-1] == '_' and
             name[1:2] != '_' and
             name[-2:-1] != '_')
 
diff -r 9d4e0445cdce Lib/test/test_enum.py
--- a/Lib/test/test_enum.py	Thu Oct 03 14:39:39 2013 -0600
+++ b/Lib/test/test_enum.py	Thu Oct 03 23:00:36 2013 +0100
@@ -58,6 +58,39 @@
 except Exception:
     pass
 
+
+class TestHelpers(unittest.TestCase):
+    """
+    _is_descriptor
+    _is_sunder
+    _is_dunder
+
+    Are private helper methods enforcing naming syntax.
+    """
+
+    def test_is_descriptor(self):
+        class foo:
+            pass
+        for attr in ('__get__','__set__','__delete__'):
+            obj = foo()
+            self.assertFalse(enum._is_descriptor(obj))
+            setattr(obj, attr, 1)
+            self.assertTrue(enum._is_descriptor(obj))
+            
+    def test_is_sunder(self):
+        for s in '_a_ _aa_'.split():
+            self.assertTrue(enum._is_sunder(s))
+
+        for s in 'a a_ _a __a a__ __a__ _a__ __a_ _ __ ___'.split():
+            self.assertFalse(enum._is_sunder(s))
+
+    def test_is_dunder(self):
+        for s in '__a__ __aa__'.split():
+            assert enum._is_dunder(s)
+
+        for s in 'a a_ a__ __a __a_ _ __ ___'.split():
+            assert not enum._is_dunder(s)
+
 class TestEnum(unittest.TestCase):
     def setUp(self):
         class Season(Enum):