diff --git a/nnunetv2/inference/predict_from_raw_data.py b/nnunetv2/inference/predict_from_raw_data.py
index c28b41e1b..8d4096482 100644
--- a/nnunetv2/inference/predict_from_raw_data.py
+++ b/nnunetv2/inference/predict_from_raw_data.py
@@ -96,7 +96,9 @@ def initialize_from_trained_model_folder(self, model_training_output_dir: str,
         num_input_channels = determine_num_input_channels(plans_manager, configuration_manager, dataset_json)
         trainer_class = recursive_find_python_class(join(nnunetv2.__path__[0], "training", "nnUNetTrainer"),
                                                     trainer_name, 'nnunetv2.training.nnUNetTrainer')
-
+        if trainer_class is None:
+            raise RuntimeError(f'Unable to locate trainer class {trainer_name} in nnunetv2.training.nnUNetTrainer. '
+                               f'Please place it there (in any .py file)!')
         network = trainer_class.build_network_architecture(
             configuration_manager.network_arch_class_name,
             configuration_manager.network_arch_init_kwargs,
diff --git a/nnunetv2/training/data_augmentation/custom_transforms/region_based_training.py b/nnunetv2/training/data_augmentation/custom_transforms/region_based_training.py
index 93e8f5edb..eb45d26f2 100644
--- a/nnunetv2/training/data_augmentation/custom_transforms/region_based_training.py
+++ b/nnunetv2/training/data_augmentation/custom_transforms/region_based_training.py
@@ -26,9 +26,7 @@ def __call__(self, **data_dict):
             b, c, *shape = seg.shape
             region_output = np.zeros((b, len(self.regions), *shape), dtype=bool)
             for region_id, region_labels in enumerate(self.regions):
-                if not isinstance(region_labels, (list, tuple)):
-                    region_labels = (region_labels, )
-                for label_value in region_labels:
-                    region_output[:, region_id] |= (seg[:, self.seg_channel] == label_value)
+                region_output[:, region_id] |= np.isin(seg[:, self.seg_channel], region_labels)
             data_dict[self.output_key] = region_output.astype(np.uint8, copy=False)
         return data_dict
+
diff --git a/nnunetv2/utilities/find_class_by_name.py b/nnunetv2/utilities/find_class_by_name.py
index a345d99a7..223b3acc3 100644
--- a/nnunetv2/utilities/find_class_by_name.py
+++ b/nnunetv2/utilities/find_class_by_name.py
@@ -21,4 +21,4 @@ def recursive_find_python_class(folder: str, class_name: str, current_module: st
                 tr = recursive_find_python_class(join(folder, modname), class_name, current_module=next_current_module)
             if tr is not None:
                 break
-    return tr
\ No newline at end of file
+    return tr