--- a/mercurial/revlog.py	Tue Oct 10 18:29:04 2023 +0200
+++ b/mercurial/revlog.py	Thu Oct 12 17:41:06 2023 +0100
@@ -292,6 +292,9 @@
 
     @staticmethod
     def is_inline_index(header_bytes):
+        if len(header_bytes) == 0:
+            return True
+
         header = INDEX_HEADER.unpack(header_bytes)[0]
 
         _format_flags = header & ~0xFFFF