diff --git a/qbreader/_api_utils.py b/qbreader/_api_utils.py
index 013d033..1645569 100644
--- a/qbreader/_api_utils.py
+++ b/qbreader/_api_utils.py
@@ -193,7 +193,7 @@ def normalize_cats(
     elif isinstance(unnormalized_cats, Iterable):
         for unnormalized_cat in unnormalized_cats:
             final_cats.append(Category(unnormalized_cat))
-        final_cats.append(*to_be_pushed_cats)
+        final_cats.extend(to_be_pushed_cats)
 
     final_subcats = []
     if unnormalized_subcats is None:
@@ -203,7 +203,7 @@ def normalize_cats(
     elif isinstance(unnormalized_subcats, Iterable):
         for unnormalized_subcat in unnormalized_subcats:
             final_subcats.append(Subcategory(unnormalized_subcat))
-        final_subcats.append(*to_be_pushed_subcats)
+        final_subcats.extend(to_be_pushed_subcats)
 
     return (
         normalize_enumlike(final_cats, Category),