diff --git a/qbreader/_api_utils.py b/qbreader/_api_utils.py
index c138c32..013d033 100644
--- a/qbreader/_api_utils.py
+++ b/qbreader/_api_utils.py
@@ -148,8 +148,14 @@ def category_correspondence(
     ]:
         return (Category.LITERATURE, None)
 
-    # Accounts for AlternateSubcategory.PRACTICES and AlternateSubcategory.BELIEFS
-    return (None, None)
+    if typed_alt_subcat in [
+        AlternateSubcategory.PRACTICES,
+        AlternateSubcategory.BELIEFS,
+    ]:
+        return (None, None)
+
+    # Alternate subcategory passed in isn't mapped to a category/subcategory
+    raise ValueError(f"Unmapped alternate subcategory: {typed_alt_subcat}")
 
 
 def normalize_cats(