diff --git a/acto/post_process/post_diff_test.py b/acto/post_process/post_diff_test.py
index 52a41e99cb..07b5f8e199 100644
--- a/acto/post_process/post_diff_test.py
+++ b/acto/post_process/post_diff_test.py
@@ -960,10 +960,10 @@ def __get_diff_paths(
             original_result = self.trial_to_steps[trial_basename].steps[
                 str(gen)
             ]
-            args.append((diff_test_result, original_result, self.config))
+            args.append([diff_test_result, original_result, self.config])
 
         with multiprocessing.Pool(num_workers) as pool:
-            diff_results = pool.map(self.check_diff_test_step, args)
+            diff_results = pool.starmap(self.check_diff_test_step, args)
 
             diff_result = self.check_diff_test_step(
                 diff_test_result, original_result, self.config