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 52d2fc0a3..93e8f5edb 100644
--- a/nnunetv2/training/data_augmentation/custom_transforms/region_based_training.py
+++ b/nnunetv2/training/data_augmentation/custom_transforms/region_based_training.py
@@ -22,17 +22,13 @@ def __init__(self, regions: Union[List, Tuple],
 
     def __call__(self, **data_dict):
         seg = data_dict.get(self.seg_key)
-        num_regions = len(self.regions)
         if seg is not None:
-            seg_shp = seg.shape
-            output_shape = list(seg_shp)
-            output_shape[1] = num_regions
-            region_output = np.zeros(output_shape, dtype=seg.dtype)
-            for b in range(seg_shp[0]):
-                for region_id, region_source_labels in enumerate(self.regions):
-                    if not isinstance(region_source_labels, (list, tuple)):
-                        region_source_labels = (region_source_labels, )
-                    for label_value in region_source_labels:
-                        region_output[b, region_id][seg[b, self.seg_channel] == label_value] = 1
-            data_dict[self.output_key] = region_output
+            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)
+            data_dict[self.output_key] = region_output.astype(np.uint8, copy=False)
         return data_dict