diff --git a/data_juicer/ops/grouper/naive_reverse_grouper.py b/data_juicer/ops/grouper/naive_reverse_grouper.py
index 804b17d9e..385a83821 100644
--- a/data_juicer/ops/grouper/naive_reverse_grouper.py
+++ b/data_juicer/ops/grouper/naive_reverse_grouper.py
@@ -21,6 +21,6 @@ def process(self, dataset):
 
         samples = []
         for sample in dataset:
-            samples.append(convert_dict_list_to_list_dict(sample))
+            samples.extend(convert_dict_list_to_list_dict(sample))
 
         return samples