diff --git a/fastreid/data/build.py b/fastreid/data/build.py
index fad5397..92202b2 100644
--- a/fastreid/data/build.py
+++ b/fastreid/data/build.py
@@ -19,6 +19,9 @@ _root = os.getenv("FASTREID_DATASETS", "datasets")
 
 
 def build_reid_train_loader(cfg):
+    cfg = cfg.clone()
+    cfg.defrost()
+
     train_items = list()
     for d in cfg.DATASETS.NAMES:
         dataset = DATASET_REGISTRY.get(d)(root=_root, combineall=cfg.DATASETS.COMBINEALL)
@@ -26,7 +29,6 @@ def build_reid_train_loader(cfg):
             dataset.show_train()
         train_items.extend(dataset.train)
 
-    cfg.defrost()
     iters_per_epoch = len(train_items) // cfg.SOLVER.IMS_PER_BATCH
     cfg.SOLVER.MAX_ITER *= iters_per_epoch
     train_transforms = build_transforms(cfg, is_train=True)
@@ -57,6 +59,9 @@ def build_reid_train_loader(cfg):
 
 
 def build_reid_test_loader(cfg, dataset_name):
+    cfg = cfg.clone()
+    cfg.defrost()
+    
     dataset = DATASET_REGISTRY.get(dataset_name)(root=_root)
     if comm.is_main_process():
         dataset.show_test()