diff --git a/api4/post_test.go b/api4/post_test.go
index 22fd2c997f..a5cf617296 100644
--- a/api4/post_test.go
+++ b/api4/post_test.go
@@ -2686,7 +2686,7 @@ func TestSetChannelUnread(t *testing.T) {
 		checkHTTPStatus(t, r, 200, false)
 		unread, err := th.App.GetChannelUnread(c1.Id, u1.Id)
 		require.Nil(t, err)
-		assert.Equal(t, int64(1), unread.MsgCount)
+		assert.Equal(t, int64(2), unread.MsgCount)
 	})
 
 	t.Run("Unread on a private channel", func(t *testing.T) {
@@ -2694,12 +2694,12 @@ func TestSetChannelUnread(t *testing.T) {
 		assert.Equal(t, 200, r.StatusCode)
 		unread, err := th.App.GetChannelUnread(th.BasicPrivateChannel.Id, u1.Id)
 		require.Nil(t, err)
-		assert.Equal(t, int64(0), unread.MsgCount)
+		assert.Equal(t, int64(1), unread.MsgCount)
 		r = th.Client.SetPostUnread(u1.Id, pp1.Id)
 		assert.Equal(t, 200, r.StatusCode)
 		unread, err = th.App.GetChannelUnread(th.BasicPrivateChannel.Id, u1.Id)
 		require.Nil(t, err)
-		assert.Equal(t, int64(1), unread.MsgCount)
+		assert.Equal(t, int64(2), unread.MsgCount)
 	})
 
 	t.Run("Can't unread an imaginary post", func(t *testing.T) {
diff --git a/app/channel_test.go b/app/channel_test.go
index 9f1f27600a..c44c6aa307 100644
--- a/app/channel_test.go
+++ b/app/channel_test.go
@@ -1080,33 +1080,33 @@ func TestMarkChannelAsUnreadFromPost(t *testing.T) {
 		response, err := th.App.MarkChannelAsUnreadFromPost(p2.Id, u1.Id)
 		require.Nil(t, err)
 		require.NotNil(t, response)
-		assert.Equal(t, int64(3), response.MsgCount)
+		assert.Equal(t, int64(2), response.MsgCount)
 		unread, err := th.App.GetChannelUnread(c1.Id, u1.Id)
 		require.Nil(t, err)
-		assert.Equal(t, int64(1), unread.MsgCount)
-		assert.Equal(t, p2.CreateAt, response.LastViewedAt)
+		assert.Equal(t, int64(2), unread.MsgCount)
+		assert.Equal(t, p2.CreateAt-1, response.LastViewedAt)
 	})
 
 	t.Run("Unread last one", func(t *testing.T) {
 		response, err := th.App.MarkChannelAsUnreadFromPost(p3.Id, u1.Id)
 		require.Nil(t, err)
 		require.NotNil(t, response)
-		assert.Equal(t, int64(4), response.MsgCount)
+		assert.Equal(t, int64(3), response.MsgCount)
 		unread, err := th.App.GetChannelUnread(c1.Id, u1.Id)
 		require.Nil(t, err)
-		assert.Equal(t, int64(0), unread.MsgCount)
-		assert.Equal(t, p3.CreateAt, response.LastViewedAt)
+		assert.Equal(t, int64(1), unread.MsgCount)
+		assert.Equal(t, p3.CreateAt-1, response.LastViewedAt)
 	})
 
 	t.Run("Unread first one", func(t *testing.T) {
 		response, err := th.App.MarkChannelAsUnreadFromPost(p1.Id, u1.Id)
 		require.Nil(t, err)
 		require.NotNil(t, response)
-		assert.Equal(t, int64(2), response.MsgCount)
+		assert.Equal(t, int64(1), response.MsgCount)
 		unread, err := th.App.GetChannelUnread(c1.Id, u1.Id)
 		require.Nil(t, err)
-		assert.Equal(t, int64(2), unread.MsgCount)
-		assert.Equal(t, p1.CreateAt, response.LastViewedAt)
+		assert.Equal(t, int64(3), unread.MsgCount)
+		assert.Equal(t, p1.CreateAt-1, response.LastViewedAt)
 	})
 
 	t.Run("Other users are unaffected", func(t *testing.T) {
@@ -1120,19 +1120,19 @@ func TestMarkChannelAsUnreadFromPost(t *testing.T) {
 		response, err := th.App.MarkChannelAsUnreadFromPost(pp1.Id, u1.Id)
 		require.Nil(t, err)
 		require.NotNil(t, response)
-		assert.Equal(t, int64(1), response.MsgCount)
+		assert.Equal(t, int64(0), response.MsgCount)
 		unread, err := th.App.GetChannelUnread(pc1.Id, u1.Id)
 		require.Nil(t, err)
-		assert.Equal(t, int64(1), unread.MsgCount)
-		assert.Equal(t, pp1.CreateAt, response.LastViewedAt)
+		assert.Equal(t, int64(2), unread.MsgCount)
+		assert.Equal(t, pp1.CreateAt-1, response.LastViewedAt)
 
 		response, err = th.App.MarkChannelAsUnreadFromPost(pp2.Id, u1.Id)
 		assert.Nil(t, err)
-		assert.Equal(t, int64(2), response.MsgCount)
+		assert.Equal(t, int64(1), response.MsgCount)
 		unread, err = th.App.GetChannelUnread(pc1.Id, u1.Id)
 		require.Nil(t, err)
-		assert.Equal(t, int64(0), unread.MsgCount)
-		assert.Equal(t, pp2.CreateAt, response.LastViewedAt)
+		assert.Equal(t, int64(1), unread.MsgCount)
+		assert.Equal(t, pp2.CreateAt-1, response.LastViewedAt)
 	})
 
 	t.Run("Can't unread an imaginary post", func(t *testing.T) {
diff --git a/store/sqlstore/channel_store.go b/store/sqlstore/channel_store.go
index 749891d081..0f00947392 100644
--- a/store/sqlstore/channel_store.go
+++ b/store/sqlstore/channel_store.go
@@ -1841,7 +1841,9 @@ func (s SqlChannelStore) CountPostsSince(channelID string, since int64) (int64,
 // it returns a channelunread so redux can update the apps easily.
 func (s SqlChannelStore) UpdateLastViewedAtPost(unreadPost *model.Post, userID string, mentionCount int) (*model.ChannelUnreadAt, *model.AppError) {
 
-	unread, appErr := s.CountPostsSince(unreadPost.ChannelId, unreadPost.CreateAt)
+	unreadDate := unreadPost.CreateAt - 1
+
+	unread, appErr := s.CountPostsSince(unreadPost.ChannelId, unreadDate)
 	if appErr != nil {
 		return nil, appErr
 	}
@@ -1849,7 +1851,7 @@ func (s SqlChannelStore) UpdateLastViewedAtPost(unreadPost *model.Post, userID s
 	params := map[string]interface{}{
 		"mentions":     mentionCount,
 		"unreadCount":  unread,
-		"lastViewedAt": unreadPost.CreateAt,
+		"lastViewedAt": unreadDate,
 		"userId":       userID,
 		"channelId":    unreadPost.ChannelId,
 		"updatedAt":    model.GetMillis(),