diff --git a/setup.cfg b/setup.cfg
index b3495570..eee4d1f0 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -21,7 +21,7 @@ description = Cylc UI Server
 long_description_content_type=text/markdown
 long_description = file: README.md
 license = GPL
-license_files = COPYING
+license_files = COPYING,
 platforms = any
 classifiers =
     Environment :: Console