--- a/mercurial/revlog.py	Tue Oct 31 22:42:46 2023 -0700
+++ b/mercurial/revlog.py	Mon Nov 06 17:12:04 2023 +0100
@@ -1279,6 +1279,9 @@
     @staticmethod
     def is_inline_index(header_bytes):
         """Determine if a revlog is inline from the initial bytes of the index"""
+        if len(header_bytes) == 0:
+            return True
+
         header = INDEX_HEADER.unpack(header_bytes)[0]
 
         _format_flags = header & ~0xFFFF