diff --git a/consensus/types/src/sync_committee_contribution.rs b/consensus/types/src/sync_committee_contribution.rs
index c8fce78a8bb..ae92df6727e 100644
--- a/consensus/types/src/sync_committee_contribution.rs
+++ b/consensus/types/src/sync_committee_contribution.rs
@@ -21,6 +21,7 @@ pub enum Error {
 pub struct SyncCommitteeContribution<T: EthSpec> {
     pub slot: Slot,
     pub beacon_block_root: Hash256,
+    #[serde(with = "serde_utils::quoted_u64")]
     pub subcommittee_index: u64,
     pub aggregation_bits: BitVector<T::SyncSubcommitteeSize>,
     pub signature: AggregateSignature,