diff --git a/api4/user_test.go b/api4/user_test.go
index 29a9fa0849..4c4d5a80bd 100644
--- a/api4/user_test.go
+++ b/api4/user_test.go
@@ -5964,6 +5964,47 @@ func TestReadThreads(t *testing.T) {
 	})
 }
 
+func TestMarkThreadUnreadMentionCount(t *testing.T) {
+	th := Setup(t).InitBasic()
+	defer th.TearDown()
+	os.Setenv("MM_FEATUREFLAGS_COLLAPSEDTHREADS", "true")
+	defer os.Unsetenv("MM_FEATUREFLAGS_COLLAPSEDTHREADS")
+	th.App.UpdateConfig(func(cfg *model.Config) {
+		*cfg.ServiceSettings.ThreadAutoFollow = true
+		*cfg.ServiceSettings.CollapsedThreads = model.COLLAPSED_THREADS_DEFAULT_ON
+	})
+	Client := th.Client
+
+	channel := th.BasicChannel
+	user := th.BasicUser
+	user2 := th.BasicUser2
+	appErr := th.App.JoinChannel(channel, user.Id)
+	require.Nil(t, appErr)
+	appErr = th.App.JoinChannel(channel, user2.Id)
+	require.Nil(t, appErr)
+
+	rpost, _ := postAndCheck(t, Client, &model.Post{ChannelId: th.BasicChannel.Id, Message: "testMsg @" + th.BasicUser2.Username})
+	time.Sleep(1)
+	reply, _ := postAndCheck(t, Client, &model.Post{ChannelId: th.BasicChannel.Id, Message: "testReply1", RootId: rpost.Id})
+	time.Sleep(1)
+	postAndCheck(t, Client, &model.Post{ChannelId: th.BasicChannel.Id, Message: "testReply2", RootId: rpost.Id})
+
+	th.SystemAdminClient.UpdateThreadReadForUser(th.BasicUser2.Id, th.BasicTeam.Id, rpost.Id, model.GetMillis())
+
+	u, _ := th.SystemAdminClient.GetUserThreads(th.BasicUser2.Id, th.BasicTeam.Id, model.GetUserThreadsOpts{})
+	require.EqualValues(t, 0, u.TotalUnreadMentions)
+
+	th.SystemAdminClient.UpdateThreadReadForUser(th.BasicUser2.Id, th.BasicTeam.Id, rpost.Id, rpost.CreateAt)
+
+	u, _ = th.SystemAdminClient.GetUserThreads(th.BasicUser2.Id, th.BasicTeam.Id, model.GetUserThreadsOpts{})
+	require.EqualValues(t, 1, u.TotalUnreadMentions)
+
+	th.SystemAdminClient.UpdateThreadReadForUser(th.BasicUser2.Id, th.BasicTeam.Id, rpost.Id, reply.CreateAt)
+
+	u, _ = th.SystemAdminClient.GetUserThreads(th.BasicUser2.Id, th.BasicTeam.Id, model.GetUserThreadsOpts{})
+	require.EqualValues(t, 0, u.TotalUnreadMentions)
+}
+
 func TestPatchAndUpdateWithProviderAttributes(t *testing.T) {
 	t.Run("LDAP user", func(t *testing.T) {
 		th := SetupEnterprise(t).InitBasic()
diff --git a/app/post.go b/app/post.go
index 8c388ee5de..4136e24bfa 100644
--- a/app/post.go
+++ b/app/post.go
@@ -1387,18 +1387,14 @@ func (a *App) countThreadMentions(user *model.User, post *model.Post, teamID str
 	if nErr != nil {
 		return 0, model.NewAppError("countMentionsFromPost", "app.channel.count_posts_since.app_error", nil, nErr.Error(), http.StatusInternalServerError)
 	}
-
-	mentions := getExplicitMentions(post, keywords, groups)
-	if post.UpdateAt >= timestamp {
-		if _, ok := mentions.Mentions[user.Id]; ok {
-			count += 1
-		}
-	}
+	posts = append(posts, post)
 
 	for _, p := range posts {
-		mentions = getExplicitMentions(p, keywords, groups)
-		if _, ok := mentions.Mentions[user.Id]; ok {
-			count += 1
+		if p.CreateAt >= timestamp {
+			mentions := getExplicitMentions(p, keywords, groups)
+			if _, ok := mentions.Mentions[user.Id]; ok {
+				count += 1
+			}
 		}
 	}