ERROR: tuple concurrently updated

Mostly a note for myself, to help me in the future, when searching the web didn’t help. I was getting this error trying to grant some privileges for a test:

postgres=> grant all privileges on all tables in schema myschema to myuser;
ERROR:  tuple concurrently updated

I have a separate service that frequently refreshes materialised views. Stopping that service temporarily appears to have allowed me to actually grant the privileges I wanted to.