diff --git a/Lib/plat-mac/applesingle.py b/Lib/plat-mac/applesingle.py
index b035d9e..76bdb06 100644
--- a/Lib/plat-mac/applesingle.py
+++ b/Lib/plat-mac/applesingle.py
@@ -25,7 +25,7 @@
     pass
 
 # File header format: magic, version, unused, number of entries
-AS_HEADER_FORMAT=">ll16sh"
+AS_HEADER_FORMAT=">LL16sh"
 AS_HEADER_LENGTH=26
 # The flag words for AppleSingle
 AS_MAGIC=0x00051600