diff --git a/lib/src/default_revset_engine.rs b/lib/src/default_revset_engine.rs
index cbd59520f..39da2f398 100644
--- a/lib/src/default_revset_engine.rs
+++ b/lib/src/default_revset_engine.rs
@@ -71,6 +71,14 @@ impl<'index> RevsetImpl<'index> {
     }
 }
 
+impl fmt::Debug for RevsetImpl<'_> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("RevsetImpl")
+            .field("inner", &self.inner)
+            .finish_non_exhaustive()
+    }
+}
+
 impl<'index> Revset<'index> for RevsetImpl<'index> {
     fn iter(&self) -> Box<dyn Iterator<Item = CommitId> + '_> {
         Box::new(self.inner.iter().map(|index_entry| index_entry.commit_id()))
diff --git a/lib/src/revset.rs b/lib/src/revset.rs
index 8b32027f4..677f74cf4 100644
--- a/lib/src/revset.rs
+++ b/lib/src/revset.rs
@@ -1654,7 +1654,7 @@ pub fn resolve_symbols(
     )
 }
 
-pub trait Revset<'index> {
+pub trait Revset<'index>: fmt::Debug {
     /// Iterate in topological order with children before parents.
     fn iter(&self) -> Box<dyn Iterator<Item = CommitId> + '_>;