diff --git a/Lib/zipfile.py b/Lib/zipfile.py
index 46328f5..a0beae2 100644
--- a/Lib/zipfile.py
+++ b/Lib/zipfile.py
@@ -384,7 +384,7 @@
         # 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: