diff -r 8cb1a561c5ac -r 3bfd80a277be rust/hg-pyo3/src/revlog/mod.rs
--- a/rust/hg-pyo3/src/revlog/mod.rs	Mon Dec 23 21:46:51 2024 +0100
+++ b/rust/hg-pyo3/src/revlog/mod.rs	Mon Dec 23 23:42:06 2024 +0100
@@ -419,6 +419,16 @@
         Ok(())
     }
 
+    /// return a binary packed version of the header
+    fn _index_pack_header(
+        slf: &Bound<'_, Self>,
+        header: i32,
+    ) -> PyResult<Py<PyBytes>> {
+        let packed =
+            Self::with_index_read(slf, |idx| Ok(idx.pack_header(header)))?;
+        Ok(PyBytes::new(slf.py(), &packed).unbind())
+    }
+
     /// reachableroots
     #[pyo3(signature = (*args))]
     fn _index_reachableroots2(