diff --git a/recommenders/models/deeprec/DataModel/ImplicitCF.py b/recommenders/models/deeprec/DataModel/ImplicitCF.py
index 5a9174312..42bb319c4 100644
--- a/recommenders/models/deeprec/DataModel/ImplicitCF.py
+++ b/recommenders/models/deeprec/DataModel/ImplicitCF.py
@@ -206,7 +206,8 @@ def train_loader(self, batch_size):
         """
 
         def sample_neg(x):
-            assert len(x) < self.n_items, "A user has voted in every item. Can't find a negative sample"
+            if len(x) >= self.n_items:
+                raise ValueError("A user has voted in every item. Can't find a negative sample.")
             while True:
                 neg_id = random.randint(0, self.n_items - 1)
                 if neg_id not in x: