diff --git a/Lib/mailbox.py b/Lib/mailbox.py
index 520afeb..3f7a12a 100755
--- a/Lib/mailbox.py
+++ b/Lib/mailbox.py
@@ -459,7 +459,11 @@
         """Update table of contents mapping."""
         self._toc = {}
         for subdir in ('new', 'cur'):
-            for entry in os.listdir(os.path.join(self._path, subdir)):
+            subdir_path = os.path.join(self._path, subdir)
+            for entry in os.listdir(subdir_path):
+                p = os.path.join(subdir_path, entry)
+                if os.path.isdir(p):
+                    continue
                 uniq = entry.split(self.colon)[0]
                 self._toc[uniq] = os.path.join(subdir, entry)
 
diff --git a/Lib/test/test_mailbox.py b/Lib/test/test_mailbox.py
index 175c291..684aeb2 100644
--- a/Lib/test/test_mailbox.py
+++ b/Lib/test/test_mailbox.py
@@ -686,7 +686,18 @@
         folder1_alias = box.get_folder('folder1')
         self.assert_(folder1_alias._factory is dummy_factory)
 
+    def test_directory_in_folder (self):
+        # Test that mailboxes still work if there's a stray extra directory
+        # in a folder.
+        for i in range(10):
+            self._box.add(mailbox.Message(_sample_message))
 
+        # Create a stray directory
+        os.mkdir(os.path.join(self._path, 'cur', 'stray-dir'))
+
+        # Check that looping still works with the directory present.
+        for msg in self._box:
+            pass
 
 class _TestMboxMMDF(TestMailbox):