diff --git a/falcon/hooks.py b/falcon/hooks.py
index 021984a25..184a302d7 100644
--- a/falcon/hooks.py
+++ b/falcon/hooks.py
@@ -329,7 +329,7 @@ def do_before(
 
 
 def _merge_responder_args(
-    args: Tuple[Any, ...], kwargs: Dict[str, Any], argnames: List[Any]
+    args: Tuple[Any, ...], kwargs: Dict[str, Any], argnames: List[str]
 ) -> None:
     """Merge responder args into kwargs.