diff --git a/mvcc/downgrade.go b/mvcc/downgrade.go
index 610ac90ce128..84f856a99fcf 100644
--- a/mvcc/downgrade.go
+++ b/mvcc/downgrade.go
@@ -38,7 +38,7 @@ func downgradeMetaBucket(lg *zap.Logger, tx backend.BatchTx) {
 	if lg != nil {
 		lg.Info(
 			"downgrade meta bucket",
-			zap.String("remove-keys", string(confStateKeyName)+","+string(termKeyName)),
+			zap.ByteStrings("remove-keys", [][]byte{confStateKeyName, termKeyName}),
 		)
 	} else {
 		plog.Printf("downgrade meta bucket: remove keys [%s, %s]", string(confStateKeyName), string(termKeyName))