diff --git a/rust/hg-core/src/revlog/index.rs b/rust/hg-core/src/revlog/index.rs
--- a/rust/hg-core/src/revlog/index.rs
+++ b/rust/hg-core/src/revlog/index.rs
@@ -131,9 +131,8 @@
         if let Some(offset_override) = self.offset_override {
             offset_override
         } else {
-            let mut bytes = [0; 8];
-            bytes[2..8].copy_from_slice(&self.bytes[0..=5]);
-            BigEndian::read_u64(&bytes[..]) as usize
+            ((BigEndian::read_u16(&self.bytes[0..2]) as usize) << 32)
+                + (BigEndian::read_u32(&self.bytes[2..6]) as usize)
         }
     }