diff --git a/core/types/receipt.go b/core/types/receipt.go
index 68dc6ab98..554513505 100644
--- a/core/types/receipt.go
+++ b/core/types/receipt.go
@@ -432,10 +432,10 @@ func (rs Receipts) EncodeIndex(i int, w *bytes.Buffer) {
 func (r Receipts) DeriveFields(hash common.Hash, number uint64, txs Transactions, senders []common.Address) error {
 	logIndex := uint(0) // logIdx is unique within the block and starts from 0
 	if len(txs) != len(r) {
-		return errors.New("transaction and receipt count mismatch")
+		return fmt.Errorf("transaction and receipt count mismatch, tx count = %d, receipts count = %d", len(txs), len(r))
 	}
 	if len(senders) != len(txs) {
-		return errors.New("transaction and senders count mismatch")
+		return fmt.Errorf("transaction and senders count mismatch, tx count = %d, receipts count = %d", len(txs), len(r))
 	}
 	for i := 0; i < len(r); i++ {
 		// The transaction type and hash can be retrieved from the transaction itself
diff --git a/ethdb/privateapi/ethbackend.go b/ethdb/privateapi/ethbackend.go
index d43667226..ce99eeaf4 100644
--- a/ethdb/privateapi/ethbackend.go
+++ b/ethdb/privateapi/ethbackend.go
@@ -216,8 +216,8 @@ func (s *EthBackendServer) Block(ctx context.Context, req *remote.BlockRequest)
 		return nil, err
 	}
 	sendersBytes := make([]byte, 20*len(senders))
-	for i := range senders {
-		sendersBytes = append(sendersBytes, senders[i][:]...)
+	for i, sender := range senders {
+		copy(sendersBytes[i*20:], sender[:])
 	}
 	return &remote.BlockReply{BlockRlp: blockRlp, Senders: sendersBytes}, nil
 }