How do I gracefully shutdown celery's flower?

Question

When I send a SIGTERM, some times flower will die with this exception & its database does not contain the latest tasks.

File "/home/devil/envs/celery/lib/python3.6/
site-packages/flower/app.py", line 68, in stop
    self.events.stop()
File "/home/devil/envs/celery/lib/python3.6/
site-packages/flower/events.py", line 98, in stop
    state['events'] = self.state
File "/usr/lib/python3.6/shelve.py", 
line 124, in __setitem__
    p.dump(value)
RuntimeError: OrderedDict mutated during iteration

Is there any way to gracefully shutdown flower ?