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
@@ -1053,7 +1053,9 @@ impl Index {
 
         let revisions: Vec<Revision> = as_set.into_iter().collect();
 
-        if revisions.len() <= 63 {
+        if revisions.len() < 8 {
+            self.find_gca_candidates::<u8>(&revisions)
+        } else if revisions.len() < 64 {
             self.find_gca_candidates::<u64>(&revisions)
         } else {
             self.find_gca_candidates::<NonStaticPoisonableBitSet>(&revisions)
@@ -1314,6 +1316,7 @@ trait PoisonableBitSet: Sized + PartialE
 }
 
 const U64_POISON: u64 = 1 << 63;
+const U8_POISON: u8 = 1 << 7;
 
 impl PoisonableBitSet for u64 {
     fn vec_of_empty(_sets_size: usize, vec_len: usize) -> Vec<Self> {
@@ -1361,6 +1364,52 @@ impl PoisonableBitSet for u64 {
     }
 }
 
+impl PoisonableBitSet for u8 {
+    fn vec_of_empty(_sets_size: usize, vec_len: usize) -> Vec<Self> {
+        vec![0; vec_len]
+    }
+
+    fn size(&self) -> usize {
+        1
+    }
+
+    fn capacity(&self) -> usize {
+        7
+    }
+
+    fn add(&mut self, n: usize) {
+        (*self) |= 1 << n;
+    }
+
+    fn discard(&mut self, n: usize) {
+        (*self) &= u8::MAX - (1 << n);
+    }
+
+    fn union(&mut self, other: &Self) {
+        if *self != *other {
+            (*self) |= *other;
+        }
+    }
+
+    fn is_full_range(&self, n: usize) -> bool {
+        *self + 1 == (1 << n)
+    }
+
+    fn is_empty(&self) -> bool {
+        *self == 0
+    }
+
+    fn poison(&mut self) {
+        *self = U8_POISON;
+    }
+
+    fn is_poisoned(&self) -> bool {
+        // equality comparison would be tempting but would not resist
+        // operations after poisoning (even if these should be bogus).
+        *self >= U8_POISON
+    }
+}
+
 /// A poisonable bit set whose capacity is not known at compile time but
 /// is constant after initial construction
 ///
diff --git a/rust/hg-cpython/src/revlog.rs b/rust/hg-cpython/src/revlog.rs
--- a/rust/hg-cpython/src/revlog.rs
+++ b/rust/hg-cpython/src/revlog.rs
@@ -20,7 +20,10 @@ use cpython::{
 };
 use hg::{
     errors::HgError,
-    index::{IndexHeader, Phase, RevisionDataParams, SnapshotsCache},
+    index::{
+        IndexHeader, Phase, RevisionDataParams, SnapshotsCache,
+        INDEX_ENTRY_SIZE,
+    },
     nodemap::{Block, NodeMapError, NodeTree},
     revlog::{nodemap::NodeMap, NodePrefix, RevlogError, RevlogIndex},
     BaseRevision, Revision, UncheckedRevision, NULL_REVISION,
@@ -483,12 +486,26 @@ py_class!(pub class MixedIndex |py| {
 
     @property
     def entry_size(&self) -> PyResult<PyInt> {
-        self.cindex(py).borrow().inner().getattr(py, "entry_size")?.extract::<PyInt>(py)
+        let rust_res: PyInt = INDEX_ENTRY_SIZE.to_py_object(py);
+
+        let c_res = self.cindex(py).borrow().inner()
+            .getattr(py, "entry_size")?;
+        assert_py_eq(py, "entry_size", rust_res.as_object(), &c_res)?;
+
+        Ok(rust_res)
     }
 
     @property
     def rust_ext_compat(&self) -> PyResult<PyInt> {
-        self.cindex(py).borrow().inner().getattr(py, "rust_ext_compat")?.extract::<PyInt>(py)
+        // will be entirely removed when the Rust index yet useful to
+        // implement in Rust to detangle things when removing `self.cindex`
+        let rust_res: PyInt = 1.to_py_object(py);
+
+        let c_res = self.cindex(py).borrow().inner()
+            .getattr(py, "rust_ext_compat")?;
+        assert_py_eq(py, "rust_ext_compat", rust_res.as_object(), &c_res)?;
+
+        Ok(rust_res)
     }
 
 });
@@ -671,7 +688,7 @@ impl MixedIndex {
         let rust_index_len = self.index(py).borrow().len();
         let cindex_len = self.cindex(py).borrow().inner().len(py)?;
         assert_eq!(rust_index_len, cindex_len);
-        Ok(cindex_len)
+        Ok(rust_index_len)
     }
 
     /// This is scaffolding at this point, but it could also become