diff -r 27e773aa607d -r 4c5f6e95df84 rust/hg-cpython/src/conversion.rs
--- a/rust/hg-cpython/src/conversion.rs	Thu Aug 10 11:01:07 2023 +0200
+++ b/rust/hg-cpython/src/conversion.rs	Fri Aug 18 14:34:29 2023 +0200
@@ -8,8 +8,10 @@
 //! Bindings for the hg::ancestors module provided by the
 //! `hg-core` crate. From Python, this will be seen as `rustext.ancestor`
 
-use cpython::{ObjectProtocol, PyObject, PyResult, Python};
-use hg::Revision;
+use cpython::{ObjectProtocol, PyErr, PyObject, PyResult, Python};
+use hg::{Revision, RevlogIndex, UncheckedRevision};
+
+use crate::{exceptions::GraphError, PyRevision};
 
 /// Utility function to convert a Python iterable into various collections
 ///
@@ -17,11 +19,28 @@
 /// with `impl IntoIterator<Item=Revision>` arguments, because
 /// a `PyErr` can arise at each step of iteration, whereas these methods
 /// expect iterables over `Revision`, not over some `Result<Revision, PyErr>`
-pub fn rev_pyiter_collect<C>(py: Python, revs: &PyObject) -> PyResult<C>
+pub fn rev_pyiter_collect<C, I>(
+    py: Python,
+    revs: &PyObject,
+    index: &I,
+) -> PyResult<C>
 where
     C: FromIterator<Revision>,
+    I: RevlogIndex,
 {
     revs.iter(py)?
-        .map(|r| r.and_then(|o| o.extract::<Revision>(py)))
+        .map(|r| {
+            r.and_then(|o| match o.extract::<PyRevision>(py) {
+                Ok(r) => index
+                    .check_revision(UncheckedRevision(r.0))
+                    .ok_or_else(|| {
+                        PyErr::new::<GraphError, _>(
+                            py,
+                            ("InvalidRevision", r.0),
+                        )
+                    }),
+                Err(e) => Err(e),
+            })
+        })
         .collect()
 }