diff --git a/src/tox/config/loader/api.py b/src/tox/config/loader/api.py
index 4d21d348e3..0349216e0a 100644
--- a/src/tox/config/loader/api.py
+++ b/src/tox/config/loader/api.py
@@ -133,7 +133,8 @@ def load(  # noqa: PLR0913
             if isinstance(converted, list) and isinstance(appends, list):
                 converted += appends
             else:
-                raise ValueError("Only able to append to lists")
+                msg = "Only able to append to lists"
+                raise ValueError(msg)
         return converted
 
     def build(  # noqa: PLR0913