diff --git a/lib/src/default_revset_engine.rs b/lib/src/default_revset_engine.rs
index eaa6034c6..ee05fa037 100644
--- a/lib/src/default_revset_engine.rs
+++ b/lib/src/default_revset_engine.rs
@@ -121,6 +121,10 @@ impl<'index> Revset<'index> for RevsetImpl<'index> {
     fn is_empty(&self) -> bool {
         self.iter().next().is_none()
     }
+
+    fn count(&self) -> usize {
+        self.inner.iter().count()
+    }
 }
 
 struct ChangeIdIndexImpl<'index> {
diff --git a/lib/src/revset.rs b/lib/src/revset.rs
index 08f155334..f64375419 100644
--- a/lib/src/revset.rs
+++ b/lib/src/revset.rs
@@ -2037,6 +2037,8 @@ pub trait Revset<'index>: fmt::Debug {
     fn change_id_index(&self) -> Box<dyn ChangeIdIndex + 'index>;
 
     fn is_empty(&self) -> bool;
+
+    fn count(&self) -> usize;
 }
 
 pub trait ChangeIdIndex: Send + Sync {