diff --git a/setup.cfg b/setup.cfg
index bc1f1399..0c78a591 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -60,5 +60,5 @@ implicit_reexport = True
 
 [mypy-jedi.debug]
 # jedi.debug is configured by setting module-level values, which mypy doesn't
-# know about.
+# know about. See https://github.com/python/mypy/issues/9209.
 warn_unreachable = False