diff --git a/federated_learning/breast_density_challenge/code/pt/learners/mammo_learner.py b/federated_learning/breast_density_challenge/code/pt/learners/mammo_learner.py
index eca65f5553..19a312ca80 100644
--- a/federated_learning/breast_density_challenge/code/pt/learners/mammo_learner.py
+++ b/federated_learning/breast_density_challenge/code/pt/learners/mammo_learner.py
@@ -238,7 +238,7 @@ def initialize(self, parts: dict, fl_ctx: FLContext):
             base_dir=self.dataset_root,
         )
 
-        num_workers = 1
+        num_workers = 4  # tuned for challenge system. Please do not change.
         cache_rate = 1.0
         self.train_dataset = CacheDataset(
             data=train_datalist,