diff --git a/src/fast_forward/util/pyterrier.py b/src/fast_forward/util/pyterrier.py
index 3523a33..e4365da 100644
--- a/src/fast_forward/util/pyterrier.py
+++ b/src/fast_forward/util/pyterrier.py
@@ -35,6 +35,7 @@ def transform(self, inp: "pd.DataFrame") -> "pd.DataFrame":
             Ranking(
                 inp.rename(columns={"qid": "q_id", "docno": "id"}),
                 copy=False,
+                # since this ranking is only used for scoring, sorting is not necessary
                 is_sorted=True,
             )
         )._df.rename(columns={"q_id": "qid", "id": "docno"})