diff --git a/ms2query/create_new_library/train_models.py b/ms2query/create_new_library/train_models.py
index f0f53d17..7b0a267f 100644
--- a/ms2query/create_new_library/train_models.py
+++ b/ms2query/create_new_library/train_models.py
@@ -33,7 +33,7 @@ def __init__(self,
         self.ms2ds_epochs: int = default_settings["ms2ds_epochs"]
         self.ms2query_fraction_for_making_pairs: int = default_settings["ms2query_fraction_for_making_pairs"]
         self.spec2vec_iterations = default_settings["spec2vec_iterations"]
-        self.add_compound_classes = default_settings["add_compound_classes"]
+        self.add_compound_classes: bool = default_settings["add_compound_classes"]
 
 
 def train_all_models(annotated_training_spectra,