diff --git a/store/sqlstore/post_store.go b/store/sqlstore/post_store.go
index b500a8c6ff..7762f7d4fa 100644
--- a/store/sqlstore/post_store.go
+++ b/store/sqlstore/post_store.go
@@ -2402,11 +2402,21 @@ func (s *SqlPostStore) updateThreadsFromPosts(transaction *gorp.Transaction, pos
 
 	for rootId, posts := range postsByRoot {
 		if thread, found := threadByRoot[rootId]; !found {
+			var data []struct {
+				UserId    string `db:"userid"`
+				RepliedAt int64  `db:"mc"`
+			}
+
 			// calculate participants
-			var participants model.StringArray
-			if _, err := transaction.Select(&participants, "SELECT DISTINCT UserId FROM Posts WHERE RootId=:RootId OR Id=:RootId", map[string]interface{}{"RootId": rootId}); err != nil {
+			if _, err := transaction.Select(&data, "SELECT UserId, MAX(CreateAt) as mc FROM Posts WHERE RootId=:RootId AND DeleteAt=0 GROUP BY UserId ORDER BY mc ASC", map[string]interface{}{"RootId": rootId}); err != nil {
 				return err
 			}
+
+			var participants model.StringArray
+			for _, item := range data {
+				participants = append(participants, item.UserId)
+			}
+
 			// calculate reply count
 			count, err := transaction.SelectInt("SELECT COUNT(Id) FROM Posts WHERE RootId=:RootId And DeleteAt=0", map[string]interface{}{"RootId": rootId})
 			if err != nil {
@@ -2431,9 +2441,10 @@ func (s *SqlPostStore) updateThreadsFromPosts(transaction *gorp.Transaction, pos
 			// metadata exists, update it
 			for _, post := range posts {
 				thread.ReplyCount += 1
-				if !thread.Participants.Contains(post.UserId) {
-					thread.Participants = append(thread.Participants, post.UserId)
+				if thread.Participants.Contains(post.UserId) {
+					thread.Participants = thread.Participants.Remove(post.UserId)
 				}
+				thread.Participants = append(thread.Participants, post.UserId)
 				if post.CreateAt > thread.LastReplyAt {
 					thread.LastReplyAt = post.CreateAt
 				}
diff --git a/store/sqlstore/thread_store.go b/store/sqlstore/thread_store.go
index 8d7d8108e7..5585addddd 100644
--- a/store/sqlstore/thread_store.go
+++ b/store/sqlstore/thread_store.go
@@ -448,6 +448,18 @@ func (s *SqlThreadStore) GetThreadForUser(teamId string, threadMembership *model
 		}
 	}
 
+	var participants []*model.User
+	for _, participantId := range thread.Participants {
+		var participant *model.User
+		for _, u := range users {
+			if u.Id == participantId {
+				participant = u
+				break
+			}
+		}
+		participants = append(participants, participant)
+	}
+
 	result := &model.ThreadResponse{
 		PostId:         thread.PostId,
 		ReplyCount:     thread.ReplyCount,
@@ -455,7 +467,7 @@ func (s *SqlThreadStore) GetThreadForUser(teamId string, threadMembership *model
 		LastViewedAt:   thread.LastViewedAt,
 		UnreadReplies:  thread.UnreadReplies,
 		UnreadMentions: thread.UnreadMentions,
-		Participants:   users,
+		Participants:   participants,
 		Post:           thread.Post.ToNilIfInvalid(),
 	}
 
diff --git a/store/storetest/post_store.go b/store/storetest/post_store.go
index 27dfe5dc5b..1619bf65bc 100644
--- a/store/storetest/post_store.go
+++ b/store/storetest/post_store.go
@@ -357,6 +357,76 @@ func testPostStoreSaveMultiple(t *testing.T, ss store.Store) {
 		assert.Greater(t, rchannel.LastPostAt, channel.LastPostAt)
 		assert.Equal(t, int64(3), rchannel.TotalMsgCount)
 	})
+
+	t.Run("Thread participants", func(t *testing.T) {
+		o1 := model.Post{}
+		o1.ChannelId = model.NewId()
+		o1.UserId = model.NewId()
+		o1.Message = "jessica hyde" + model.NewId() + "b"
+
+		root, err := ss.Post().Save(&o1)
+		require.NoError(t, err)
+
+		o2 := model.Post{}
+		o2.ChannelId = model.NewId()
+		o2.UserId = model.NewId()
+		o2.RootId = root.Id
+		o2.Message = "zz" + model.NewId() + "b"
+
+		o3 := model.Post{}
+		o3.ChannelId = model.NewId()
+		o3.UserId = model.NewId()
+		o3.RootId = root.Id
+		o3.Message = "zz" + model.NewId() + "b"
+
+		o4 := model.Post{}
+		o4.ChannelId = model.NewId()
+		o4.UserId = o2.UserId
+		o4.RootId = root.Id
+		o4.Message = "zz" + model.NewId() + "b"
+
+		o5 := model.Post{}
+		o5.ChannelId = model.NewId()
+		o5.UserId = o1.UserId
+		o5.RootId = root.Id
+		o5.Message = "zz" + model.NewId() + "b"
+
+		_, err = ss.Post().Save(&o2)
+		require.NoError(t, err)
+		thread, errT := ss.Thread().Get(root.Id)
+		require.NoError(t, errT)
+
+		assert.Equal(t, int64(1), thread.ReplyCount)
+		assert.Equal(t, int(1), len(thread.Participants))
+		assert.Equal(t, model.StringArray{o2.UserId}, thread.Participants)
+
+		_, err = ss.Post().Save(&o3)
+		require.NoError(t, err)
+		thread, errT = ss.Thread().Get(root.Id)
+		require.NoError(t, errT)
+
+		assert.Equal(t, int64(2), thread.ReplyCount)
+		assert.Equal(t, int(2), len(thread.Participants))
+		assert.Equal(t, model.StringArray{o2.UserId, o3.UserId}, thread.Participants)
+
+		_, err = ss.Post().Save(&o4)
+		require.NoError(t, err)
+		thread, errT = ss.Thread().Get(root.Id)
+		require.NoError(t, errT)
+
+		assert.Equal(t, int64(3), thread.ReplyCount)
+		assert.Equal(t, int(2), len(thread.Participants))
+		assert.Equal(t, model.StringArray{o3.UserId, o2.UserId}, thread.Participants)
+
+		_, err = ss.Post().Save(&o5)
+		require.NoError(t, err)
+		thread, errT = ss.Thread().Get(root.Id)
+		require.NoError(t, errT)
+
+		assert.Equal(t, int64(4), thread.ReplyCount)
+		assert.Equal(t, int(3), len(thread.Participants))
+		assert.Equal(t, model.StringArray{o3.UserId, o2.UserId, o1.UserId}, thread.Participants)
+	})
 }
 
 func testPostStoreSaveChannelMsgCounts(t *testing.T, ss store.Store) {
diff --git a/store/storetest/thread_store.go b/store/storetest/thread_store.go
index dc701349ac..cf02dad3c1 100644
--- a/store/storetest/thread_store.go
+++ b/store/storetest/thread_store.go
@@ -231,7 +231,7 @@ func testThreadStorePopulation(t *testing.T, ss store.Store) {
 		thread1, err := ss.Thread().Get(newPosts1[0].Id)
 		require.NoError(t, err)
 		require.EqualValues(t, thread1.ReplyCount, 1)
-		require.Len(t, thread1.Participants, 2)
+		require.Len(t, thread1.Participants, 1)
 
 		err = ss.Post().PermanentDeleteByUser(rootPost.UserId)
 		require.NoError(t, err)