Evince: Unable to init server: Could not Connect: Connection refused

When running

$ evince a.pdf

I receive the following error message.

No protocol specified
Unable to init server: Could not connect: Connection refused
Cannot parse arguments: Cannot open display:

I have an X Session running and DISPLAY=:0

Specifying the display

$ evince --display=:0

yields a similar error message

No protocol specified
Unable to init server: Could not connect: Connection refused
Cannot parse arguments: Cannot open display: :0

I am running Debian 10 Buster.