diff --git a/PIL/_util.py b/PIL/_util.py
index cdf91ce76..220ac6c52 100644
--- a/PIL/_util.py
+++ b/PIL/_util.py
@@ -1,3 +1,5 @@
+import os
+
 if bytes is str:
     def isStringType(t):
         return isinstance(t, basestring)