diff --git a/models/migrations/v68.go b/models/migrations/v68.go
index 4ac55b722..e76e5a5bd 100644
--- a/models/migrations/v68.go
+++ b/models/migrations/v68.go
@@ -29,13 +29,13 @@ func reformatAndRemoveIncorrectTopics(x *xorm.Engine) (err error) {
 	delTopicIDs := make([]int64, 0, batchSize)
 	ids := make([]int64, 0, 30)
 
+	log.Info("Validating existed topics...")
 	if err := sess.Begin(); err != nil {
 		return err
 	}
-	log.Info("Validating existed topics...")
 	for start := 0; ; start += batchSize {
 		topics = topics[:0]
-		if err := sess.Asc("id").Limit(batchSize, start).Find(&topics); err != nil {
+		if err := x.Asc("id").Limit(batchSize, start).Find(&topics); err != nil {
 			return err
 		}
 		if len(topics) == 0 {
@@ -49,7 +49,7 @@ func reformatAndRemoveIncorrectTopics(x *xorm.Engine) (err error) {
 
 			topic.Name = strings.Replace(strings.TrimSpace(strings.ToLower(topic.Name)), " ", "-", -1)
 
-			if err := sess.Table("repo_topic").Cols("repo_id").
+			if err := x.Table("repo_topic").Cols("repo_id").
 				Where("topic_id = ?", topic.ID).Find(&ids); err != nil {
 				return err
 			}
@@ -58,11 +58,21 @@ func reformatAndRemoveIncorrectTopics(x *xorm.Engine) (err error) {
 			}
 
 			if models.ValidateTopic(topic.Name) {
-				count, err := sess.Where("name = ?", topic.Name).Count(&Topic{})
+				unifiedTopic := Topic{Name:topic.Name}
+				exists, err := sess.Get(&unifiedTopic)
+				log.Info("Exists topic with the name %q? %v id = %v", topic.Name, exists, unifiedTopic.ID)
 				if err != nil {
 					return err
 				}
-				if count == 0 {
+				if exists {
+					log.Info("Updating repo_topic rows with topic_id = %v to topic_id = %v", topic.ID, unifiedTopic.ID)
+					if _, err := sess.Where("topic_id = ? AND repo_id NOT IN " +
+						"(SELECT rt1.repo_id FROM repo_topic rt1 INNER JOIN repo_topic rt2 " +
+						"ON rt1.repo_id = rt2.repo_id WHERE rt1.topic_id = ? AND rt2.topic_id = ?)",
+						topic.ID, topic.ID, unifiedTopic.ID).Update(&models.RepoTopic{TopicID:unifiedTopic.ID}); err != nil {
+						return err
+					}
+				} else {
 					log.Info("Updating topic: id = %v, name = %q", topic.ID, topic.Name)
 					if _, err := sess.Table("topic").ID(topic.ID).
 						Update(&Topic{Name: topic.Name}); err != nil {
@@ -74,8 +84,16 @@ func reformatAndRemoveIncorrectTopics(x *xorm.Engine) (err error) {
 			delTopicIDs = append(delTopicIDs, topic.ID)
 		}
 	}
+	if err := sess.Commit(); err != nil {
+		return err
+	}
+
+	sess.Init()
 
 	log.Info("Deleting incorrect topics...")
+	if err := sess.Begin(); err != nil {
+		return err
+	}
 	for start := 0; ; start += batchSize {
 		if (start + batchSize) < len(delTopicIDs) {
 			ids = delTopicIDs[start:(start + batchSize)]
@@ -97,6 +115,9 @@ func reformatAndRemoveIncorrectTopics(x *xorm.Engine) (err error) {
 			break
 		}
 	}
+	if err := sess.Commit(); err != nil {
+		return err
+	}
 
 	repoTopics := make([]*models.RepoTopic, 0, batchSize)
 	delRepoTopics := make([]*models.RepoTopic, 0, batchSize)
@@ -105,7 +126,7 @@ func reformatAndRemoveIncorrectTopics(x *xorm.Engine) (err error) {
 	log.Info("Checking the number of topics in the repositories...")
 	for start := 0; ; start += batchSize {
 		repoTopics = repoTopics[:0]
-		if err := sess.Cols("repo_id").Asc("repo_id").Limit(batchSize, start).
+		if err := x.Cols("repo_id").Asc("repo_id").Limit(batchSize, start).
 			GroupBy("repo_id").Having("COUNT(*) > 25").Find(&repoTopics); err != nil {
 			return err
 		}
@@ -118,7 +139,7 @@ func reformatAndRemoveIncorrectTopics(x *xorm.Engine) (err error) {
 			touchedRepo[repoTopic.RepoID] = struct{}{}
 
 			tmpRepoTopics = tmpRepoTopics[:0]
-			if err := sess.Where("repo_id = ?", repoTopic.RepoID).Find(&tmpRepoTopics); err != nil {
+			if err := x.Where("repo_id = ?", repoTopic.RepoID).Find(&tmpRepoTopics); err != nil {
 				return err
 			}
 
@@ -130,7 +151,12 @@ func reformatAndRemoveIncorrectTopics(x *xorm.Engine) (err error) {
 		}
 	}
 
+	sess.Init()
+
 	log.Info("Deleting superfluous topics for repositories (more than 25 topics)...")
+	if err := sess.Begin(); err != nil {
+		return err
+	}
 	for _, repoTopic := range delRepoTopics {
 		log.Info("Deleting 'repo_topic' rows for 'repository' with id = %v. Topic id = %v",
 			repoTopic.RepoID, repoTopic.TopicID)