pre_save not working in mongoengine update_one

I am using Python mongoengine and I would like to define callback, which will be called everytime document is updated.

from mongoengine import *
from mongoengine import signals
from time import time

class Item(Document):
    name = StringField()
    modified = LongField()


def update_modified(sender, document):
    document.modified = time()


signals.pre_save.connect(update_modified)

However update_modified is not called, when I update document:

Item.collection.objects(name="First").update_one(name="Second")

Is there any way to fix it?