diff --git a/supervision/dataset/core.py b/supervision/dataset/core.py
index d40728e4..15d92aa0 100644
--- a/supervision/dataset/core.py
+++ b/supervision/dataset/core.py
@@ -241,10 +241,6 @@ class DetectionDataset(BaseDataset):
             force_masks=force_masks,
         )
 
-        for annotation in annotations.values():
-            class_id = [classes.index(class_name) for class_name in annotation.class_id]
-            annotation.class_id = np.array(class_id)
-
         return DetectionDataset(classes=classes, images=images, annotations=annotations)
 
     @classmethod
diff --git a/supervision/dataset/formats/pascal_voc.py b/supervision/dataset/formats/pascal_voc.py
index 90501be3..8f3fb090 100644
--- a/supervision/dataset/formats/pascal_voc.py
+++ b/supervision/dataset/formats/pascal_voc.py
@@ -203,6 +203,10 @@ def load_pascal_voc_annotations(
 
     classes = list(set(classes))
 
+    for annotation in annotations.values():
+        class_id = [classes.index(class_name) for class_name in annotation.class_id]
+        annotation.class_id = np.array(class_id)
+
     return classes, images, annotations