diff --git a/models/topic.go b/models/topic.go
index 0b19bc1f0..ea5698f4c 100644
--- a/models/topic.go
+++ b/models/topic.go
@@ -9,6 +9,7 @@ import (
 	"regexp"
 	"strings"
 	"unicode/utf8"
+	"xorm.io/xorm"
 
 	"code.gitea.io/gitea/modules/timeutil"
 
@@ -337,3 +338,16 @@ func GetOrgTopics(orgId int64) ([]Topic, error) {
 
 	return result, nil
 }
+
+func UpdateRepoTopics(repoID int64, topicNames []string, sess ...*xorm.Engine) error {
+	e := x
+	if len(sess) > 0 {
+		e = sess[0]
+	}
+	if _, err := e.ID(repoID).Cols("topics").Update(&Repository{
+		Topics: topicNames,
+	}); err != nil {
+		return err
+	}
+	return nil
+}
diff --git a/routers/api/v1/repo/topic.go b/routers/api/v1/repo/topic.go
index f4ff7a329..d2522c9ce 100644
--- a/routers/api/v1/repo/topic.go
+++ b/routers/api/v1/repo/topic.go
@@ -177,13 +177,25 @@ func AddTopic(ctx *context.APIContext) {
 		return
 	}
 
-	_, err = models.AddTopic(ctx.Repo.Repository.ID, topicName)
+	topic, err := models.AddTopic(ctx.Repo.Repository.ID, topicName)
 	if err != nil {
 		log.Error("AddTopic failed: %v", err)
 		ctx.InternalServerError(err)
 		return
 	}
-
+	found := false
+	topicNames := make([]string, len(topics))
+	for i, t := range topics {
+		topicNames[i] = t.Name
+		if strings.EqualFold(topic.Name, t.Name) {
+			found = true
+			break
+		}
+	}
+	if !found && topic.Name != "" {
+		topicNames = append(topicNames, topic.Name)
+	}
+	models.UpdateRepoTopics(ctx.Repo.Repository.ID, topicNames)
 	ctx.Status(http.StatusNoContent)
 }