diff --git a/reco_utils/recommender/surprise/surprise_utils.py b/reco_utils/recommender/surprise/surprise_utils.py
index ad9f702b1e..21c769910f 100644
--- a/reco_utils/recommender/surprise/surprise_utils.py
+++ b/reco_utils/recommender/surprise/surprise_utils.py
@@ -96,8 +96,11 @@ def compute_ranking_predictions(
         pd.DataFrame: dataframe with usercol, itemcol, predcol
     """
     preds_lst = []
-    for user in data[usercol].unique():
-        for item in data[itemcol].unique():
+    users = data[usercol].unique()
+    items = data[itemcol].unique()
+
+    for user in users:
+        for item in items:
             preds_lst.append([user, item, algo.predict(user, item).est])
 
     all_predictions = pd.DataFrame(data=preds_lst, columns=[usercol, itemcol, predcol])