diff --git a/beacon/types/committee.go b/beacon/types/committee.go
index 9d3b9ff9e..5f89c2755 100644
--- a/beacon/types/committee.go
+++ b/beacon/types/committee.go
@@ -164,44 +164,21 @@ func (sc *SyncCommittee) VerifySignature(signingRoot common.Hash, signature *Syn
 	return bls.FastAggregateVerify(keys, signingRoot[:], &sig)
 }
 
+//go:generate go run github.com/fjl/gencodec -type SyncAggregate -field-override syncAggregateMarshaling -out gen_syncaggregate_json.go
+
 // SyncAggregate represents an aggregated BLS signature with Signers referring
 // to a subset of the corresponding sync committee.
 //
 // See data structure definition here:
 // https://github.com/ethereum/consensus-specs/blob/dev/specs/altair/beacon-chain.md#syncaggregate
 type SyncAggregate struct {
-	Signers   [params.SyncCommitteeBitmaskSize]byte
-	Signature [params.BLSSignatureSize]byte
+	Signers   [params.SyncCommitteeBitmaskSize]byte `gencodec:"required" json:"sync_committee_bits"`
+	Signature [params.BLSSignatureSize]byte         `gencodec:"required" json:"sync_committee_signature"`
 }
 
-type jsonSyncAggregate struct {
-	Signers   hexutil.Bytes `json:"sync_committee_bits"`
-	Signature hexutil.Bytes `json:"sync_committee_signature"`
-}
-
-// MarshalJSON implements json.Marshaler.
-func (s *SyncAggregate) MarshalJSON() ([]byte, error) {
-	return json.Marshal(&jsonSyncAggregate{
-		Signers:   s.Signers[:],
-		Signature: s.Signature[:],
-	})
-}
-
-// UnmarshalJSON implements json.Marshaler.
-func (s *SyncAggregate) UnmarshalJSON(input []byte) error {
-	var sc jsonSyncAggregate
-	if err := json.Unmarshal(input, &sc); err != nil {
-		return err
-	}
-	if len(sc.Signers) != params.SyncCommitteeBitmaskSize {
-		return fmt.Errorf("invalid signature bitmask size %d", len(sc.Signers))
-	}
-	if len(sc.Signature) != params.BLSSignatureSize {
-		return fmt.Errorf("invalid signature size %d", len(sc.Signature))
-	}
-	copy(s.Signers[:], sc.Signers)
-	copy(s.Signature[:], sc.Signature)
-	return nil
+type syncAggregateMarshaling struct {
+	Signers   hexutil.Bytes
+	Signature hexutil.Bytes
 }
 
 // SignerCount returns the number of signers in the aggregate signature.
diff --git a/beacon/types/gen_syncaggregate_json.go b/beacon/types/gen_syncaggregate_json.go
new file mode 100644
index 000000000..1547ec5f0
--- /dev/null
+++ b/beacon/types/gen_syncaggregate_json.go
@@ -0,0 +1,51 @@
+// Code generated by github.com/fjl/gencodec. DO NOT EDIT.
+
+package types
+
+import (
+	"encoding/json"
+	"errors"
+
+	"github.com/ethereum/go-ethereum/common/hexutil"
+)
+
+var _ = (*syncAggregateMarshaling)(nil)
+
+// MarshalJSON marshals as JSON.
+func (s SyncAggregate) MarshalJSON() ([]byte, error) {
+	type SyncAggregate struct {
+		Signers   hexutil.Bytes `gencodec:"required" json:"sync_committee_bits"`
+		Signature hexutil.Bytes `gencodec:"required" json:"sync_committee_signature"`
+	}
+	var enc SyncAggregate
+	enc.Signers = s.Signers[:]
+	enc.Signature = s.Signature[:]
+	return json.Marshal(&enc)
+}
+
+// UnmarshalJSON unmarshals from JSON.
+func (s *SyncAggregate) UnmarshalJSON(input []byte) error {
+	type SyncAggregate struct {
+		Signers   *hexutil.Bytes `gencodec:"required" json:"sync_committee_bits"`
+		Signature *hexutil.Bytes `gencodec:"required" json:"sync_committee_signature"`
+	}
+	var dec SyncAggregate
+	if err := json.Unmarshal(input, &dec); err != nil {
+		return err
+	}
+	if dec.Signers == nil {
+		return errors.New("missing required field 'sync_committee_bits' for SyncAggregate")
+	}
+	if len(*dec.Signers) != len(s.Signers) {
+		return errors.New("field 'sync_committee_bits' has wrong length, need 64 items")
+	}
+	copy(s.Signers[:], *dec.Signers)
+	if dec.Signature == nil {
+		return errors.New("missing required field 'sync_committee_signature' for SyncAggregate")
+	}
+	if len(*dec.Signature) != len(s.Signature) {
+		return errors.New("field 'sync_committee_signature' has wrong length, need 96 items")
+	}
+	copy(s.Signature[:], *dec.Signature)
+	return nil
+}