diff --git a/proto/engine/v1/json_marshal_unmarshal.go b/proto/engine/v1/json_marshal_unmarshal.go
index c172736565..c63f2d1837 100644
--- a/proto/engine/v1/json_marshal_unmarshal.go
+++ b/proto/engine/v1/json_marshal_unmarshal.go
@@ -187,7 +187,7 @@ func (e *ExecutionPayload) MarshalJSON() ([]byte, error) {
 	for i, tx := range e.Transactions {
 		transactions[i] = tx
 	}
-	baseFee := new(big.Int).SetBytes(e.BaseFeePerGas)
+	baseFee := new(big.Int).SetBytes(bytesutil.ReverseByteOrder(e.BaseFeePerGas))
 	baseFeeHex := hexutil.EncodeBig(baseFee)
 	return json.Marshal(executionPayloadJSON{
 		ParentHash:    e.ParentHash,
diff --git a/proto/engine/v1/json_marshal_unmarshal_test.go b/proto/engine/v1/json_marshal_unmarshal_test.go
index 66461c9621..ba0e4e792f 100644
--- a/proto/engine/v1/json_marshal_unmarshal_test.go
+++ b/proto/engine/v1/json_marshal_unmarshal_test.go
@@ -79,6 +79,7 @@ func TestJsonMarshalUnmarshal(t *testing.T) {
 	})
 	t.Run("execution payload", func(t *testing.T) {
 		baseFeePerGas := big.NewInt(6)
+		baseFeePerGasBytes := bytesutil.ReverseByteOrder(baseFeePerGas.Bytes())
 		parentHash := bytesutil.PadTo([]byte("parent"), fieldparams.RootLength)
 		feeRecipient := bytesutil.PadTo([]byte("feeRecipient"), fieldparams.FeeRecipientLength)
 		stateRoot := bytesutil.PadTo([]byte("stateRoot"), fieldparams.RootLength)
@@ -99,7 +100,7 @@ func TestJsonMarshalUnmarshal(t *testing.T) {
 			GasUsed:       3,
 			Timestamp:     4,
 			ExtraData:     extra,
-			BaseFeePerGas: baseFeePerGas.Bytes(),
+			BaseFeePerGas: baseFeePerGasBytes,
 			BlockHash:     hash,
 			Transactions:  [][]byte{[]byte("hi")},
 		}