diff -r 58bd6a58365d Doc/library/packaging.util.rst
--- a/Doc/library/packaging.util.rst	Wed Feb 08 04:09:37 2012 +0100
+++ b/Doc/library/packaging.util.rst	Wed Feb 08 13:49:22 2012 +0200
@@ -64,6 +64,8 @@
    in Unix style, and have to be converted to the local convention before we
    can actually use them in the filesystem.  Raises :exc:`ValueError` on
    non-Unix-ish systems if *pathname* either starts or ends with a slash.
+   Also Raises :exc:`TypeError` if 'pathname' is not a string or is not
+   ``None``.
 
 
 .. function:: change_root(new_root, pathname)
diff -r 58bd6a58365d Lib/packaging/tests/test_util.py
--- a/Lib/packaging/tests/test_util.py	Wed Feb 08 04:09:37 2012 +0100
+++ b/Lib/packaging/tests/test_util.py	Wed Feb 08 13:49:22 2012 +0200
@@ -199,6 +199,11 @@
         self.assertEqual(convert_path('.'),
                          os.curdir)
 
+        # wrong types
+        wrong_types = [False, 0, 0.0, 0j, {}, [], set()]
+        for wrong_type in wrong_types:
+            self.assertRaises(TypeError, convert_path, wrong_type)
+
     def test_change_root(self):
         # linux/mac
         os.name = 'posix'
diff -r 58bd6a58365d Lib/packaging/util.py
--- a/Lib/packaging/util.py	Wed Feb 08 04:09:37 2012 +0100
+++ b/Lib/packaging/util.py	Wed Feb 08 13:49:22 2012 +0200
@@ -104,6 +104,8 @@
     ValueError on non-Unix-ish systems if 'pathname' either starts or
     ends with a slash.
     """
+    if not isinstance(pathname, (str, type(None))):
+        raise TypeError("path name should be a string")
     if os.sep == '/':
         return pathname
     if not pathname: