diff --git a/polkadot/node/overseer/src/lib.rs b/polkadot/node/overseer/src/lib.rs
index f4eddf1f41..e16a3fd27a 100644
--- a/polkadot/node/overseer/src/lib.rs
+++ b/polkadot/node/overseer/src/lib.rs
@@ -465,7 +465,7 @@ pub async fn forward_events<P: BlockchainEvents<Block>>(client: Arc<P>, mut hand
 	message_capacity=2048,
 )]
 pub struct Overseer<SupportsParachains> {
-	#[subsystem(CandidateValidationMessage, sends: [
+	#[subsystem(blocking, CandidateValidationMessage, sends: [
 		RuntimeApiMessage,
 	])]
 	candidate_validation: CandidateValidation,