diff -r b4d1e51d91f8 Lib/zipfile.py
--- a/Lib/zipfile.py	Wed Mar 14 08:18:59 2012 +0100
+++ b/Lib/zipfile.py	Sat Mar 17 11:39:55 2012 +0200
@@ -370,7 +370,7 @@
         # Try to decode the extra field.
         extra = self.extra
         unpack = struct.unpack
-        while extra:
+        while len(extra) >= 4:
             tp, ln = unpack('<HH', extra[:4])
             if tp == 1:
                 if ln >= 24: