diff --git a/tuf/interposition/updater.py b/tuf/interposition/updater.py
index 6c83e964..5d7e148a 100644
--- a/tuf/interposition/updater.py
+++ b/tuf/interposition/updater.py
@@ -133,7 +133,7 @@ def open(self, url, data=None):
     filename, headers = self.retrieve(url, data=data)
 
     # TODO: like tempfile, ensure file is deleted when closed?
-    temporary_file = open(filename)
+    temporary_file = open(filename, 'rb')
 
     # extend temporary_file with info(), getcode(), geturl()
     # http://docs.python.org/2/library/urllib.html#urllib.urlopen