diff --git a/marshmallow_jsonschema/base.py b/marshmallow_jsonschema/base.py
index 700cae4..3643ff4 100644
--- a/marshmallow_jsonschema/base.py
+++ b/marshmallow_jsonschema/base.py
@@ -127,6 +127,7 @@ def _resolve_additional_properties(cls) -> bool:
     elif unknown == INCLUDE:
         return True
     else:
+        # This is probably unreachable as of marshmallow 3.16.0
         raise UnsupportedValueError("Unknown value %s for `unknown`" % unknown)