diff -r a9f7c2d49149 Lib/posixpath.py
--- a/Lib/posixpath.py	Tue Jul 16 22:11:28 2013 +0300
+++ b/Lib/posixpath.py	Mon Jul 22 09:32:37 2013 -0700
@@ -10,6 +10,7 @@
 for manipulation of the pathname component of URLs.
 """
 
+import errno
 import os
 import sys
 import stat
@@ -188,14 +189,21 @@
 
 def ismount(path):
     """Test whether a path is a mount point"""
-    if islink(path):
-        # A symlink can never be a mount point
-        return False
+    # We inline islink so we don't perform an extra lstat syscall.
     try:
         s1 = os.lstat(path)
+    except os.error:
+        # It doesn't exist -- so not a mount point :-)
+        return False
+    else:
+        # A symlink can never be a mount point
+        if stat.S_ISLNK(s1.st_mode):
+            return False
+
+    try:
         s2 = os.lstat(join(path, '..'))
     except os.error:
-        return False # It doesn't exist -- so not a mount point :-)
+        return False
     dev1 = s1.st_dev
     dev2 = s2.st_dev
     if dev1 != dev2: