diff --git a/recbole/utils/case_study.py b/recbole/utils/case_study.py
index 3775b4a3e..7b7d8b5c7 100644
--- a/recbole/utils/case_study.py
+++ b/recbole/utils/case_study.py
@@ -43,7 +43,11 @@ def full_sort_scores(uid_series, model, test_data, device=None):
 
     if not test_data.is_sequential:
         input_interaction = dataset.join(Interaction({uid_field: uid_series}))
-        history_item = test_data.uid2history_item[uid_series]
+        if len(uid_series) == 1:
+            history_item = np.array([None])
+            history_item[0] = test_data.uid2history_item[uid_series]
+        else:
+            history_item = test_data.uid2history_item[uid_series]
         history_row = torch.cat([torch.full_like(hist_iid, i) for i, hist_iid in enumerate(history_item)])
         history_col = torch.cat(list(history_item))
         history_index = history_row, history_col