Added missing import.
diff --git a/Lib/posixpath.py b/Lib/posixpath.py
index 128a533..81f25b8 100644
--- a/Lib/posixpath.py
+++ b/Lib/posixpath.py
@@ -11,6 +11,7 @@
 """
 
 import os
+import sys
 import stat
 import genericpath
 import warnings