diff --git a/internal/querylog/csv.go b/internal/querylog/csv.go
index 7a4016f4..dd7ceec8 100644
--- a/internal/querylog/csv.go
+++ b/internal/querylog/csv.go
@@ -10,7 +10,7 @@ import (
 )
 
 // csvHeaderRow is a slice of strings with row names for CSV header.  This
-// const should correspond with [logEntry.toCSV] func.
+// slice should correspond with [logEntry.toCSV] func.
 var csvHeaderRow = []string{
 	"ans_dnssec",
 	"ans_rcode",
@@ -46,7 +46,7 @@ func (e *logEntry) toCSV() (out []string) {
 	aData := ansData(e)
 
 	return []string{
-		aData.dnsSec,
+		strconv.FormatBool(e.AuthenticatedData),
 		aData.rCode,
 		aData.typ,
 		aData.value,
@@ -69,10 +69,9 @@ func (e *logEntry) toCSV() (out []string) {
 
 // csvAnswer is a helper struct for csv row answer fields.
 type csvAnswer struct {
-	dnsSec string
-	rCode  string
-	typ    string
-	value  string
+	rCode string
+	typ   string
+	value string
 }
 
 // ansData returns a map with message answer data.
@@ -90,10 +89,6 @@ func ansData(entry *logEntry) (out csvAnswer) {
 
 	out.rCode = dns.RcodeToString[msg.Rcode]
 
-	// Old query logs may still keep AD flag value in the message.  Try to get
-	// it from there as well.
-	out.dnsSec = strconv.FormatBool(entry.AuthenticatedData || msg.AuthenticatedData)
-
 	if len(msg.Answer) == 0 {
 		return out
 	}
diff --git a/internal/querylog/http.go b/internal/querylog/http.go
index 97e7d4cd..e3d9a19a 100644
--- a/internal/querylog/http.go
+++ b/internal/querylog/http.go
@@ -99,6 +99,11 @@ func (l *queryLog) handleQueryLog(w http.ResponseWriter, r *http.Request) {
 	_ = aghhttp.WriteJSONResponse(w, r, resp)
 }
 
+// exportChunkSize is a size of one search-flush iteration for query log export.
+//
+// TODO(a.meshkov): Consider making configurable.
+const exportChunkSize = 500
+
 // handleQueryLogExport is the handler for the GET /control/querylog/export
 // HTTP API.
 func (l *queryLog) handleQueryLogExport(w http.ResponseWriter, r *http.Request) {
@@ -110,8 +115,7 @@ func (l *queryLog) handleQueryLogExport(w http.ResponseWriter, r *http.Request)
 	}
 
 	params := &searchParams{
-		// TODO(a.meshkov): Consider making configurable.
-		limit:          500,
+		limit:          exportChunkSize,
 		searchCriteria: searchCriteria,
 	}
 
@@ -119,12 +123,6 @@ func (l *queryLog) handleQueryLogExport(w http.ResponseWriter, r *http.Request)
 	w.Header().Set(httphdr.ContentDisposition, "attachment;filename=data.csv")
 
 	csvWriter := csv.NewWriter(w)
-	defer func() {
-		if err = csvWriter.Error(); err != nil {
-			// TODO(a.garipov): Set Trailer X-Error header.
-			log.Error("%s %s %s: %s", r.Method, r.Host, r.URL, "writing csv")
-		}
-	}()
 
 	// Write header.
 	if err = csvWriter.Write(csvHeaderRow); err != nil {
@@ -160,6 +158,11 @@ func (l *queryLog) handleQueryLogExport(w http.ResponseWriter, r *http.Request)
 
 		csvWriter.Flush()
 	}
+
+	if err = csvWriter.Error(); err != nil {
+		// TODO(a.garipov): Set Trailer X-Error header.
+		log.Error("%s %s %s: %s", r.Method, r.Host, r.URL, "writing csv")
+	}
 }
 
 // handleQueryLogClear is the handler for the POST /control/querylog/clear HTTP
diff --git a/openapi/CHANGELOG.md b/openapi/CHANGELOG.md
index b85fa7d9..863c8f57 100644
--- a/openapi/CHANGELOG.md
+++ b/openapi/CHANGELOG.md
@@ -11,7 +11,7 @@
 * The new `GET /control/querylog/export` HTTP API allows an export of query log
   items in the CSV file.  It returns a CSV object with the following format:
 
-```text
+```csv
 ans_dnssec,ans_rcode,ans_type,ans_value,cached,client_ip,client_id,ecs,elapsed,filter_id,filter_rule,proto,qclass,qname,qtype,reason,time,upstream
 false,NOERROR,A,192.168.1.1,false,127.0.0.1,,,0.097409,,,,IN,example.com,A,Rewrite,2023-01-30T12:21:13.947563+07:00,
 false,NOERROR,A,45.33.2.79,false,127.0.0.1,,,482.967871,,,,IN,test.com,A,NotFilteredNotFound,2022-12-13T12:18:04.964403+07:00,https://dns10.quad9.net:443/dns-query