diff --git a/openpecha/serializers/serialize.py b/openpecha/serializers/serialize.py
index d4ef275f..d96becc7 100644
--- a/openpecha/serializers/serialize.py
+++ b/openpecha/serializers/serialize.py
@@ -210,12 +210,13 @@ def apply_index(self):
         for ann_id, topic in self.index_layer["annotations"].items():
             topic_ann = defaultdict(str)
             sub_topics = topic["parts"]
-            for i, sub_topic in enumerate(sub_topics):
-                if sub_topic:
-                    vol_id = f"v{sub_topic['span']['vol']:03}"
-                    sub_topic["type"] = AnnType.sub_topic
-                    if sub_topic["work_id"] != sub_topics[i - 1]["work_id"]:
-                        self.apply_annotation(vol_id, sub_topic)
+            for sub_topic_uuid, sub_topic in sub_topics.items():
+                sub_topic_ann = defaultdict(str)
+                vol_id = f"v{sub_topic['span'][0]['vol']:03}"
+                sub_topic_ann["type"] = AnnType.sub_topic
+                sub_topic_ann["work_id"] = sub_topic["work_id"]
+                sub_topic_ann["span"] = sub_topic['span'][0]
+                self.apply_annotation(vol_id, sub_topic_ann)
             if topic["span"]:
                 vol_id = f"v{topic['span'][0]['vol']:03}"
                 topic_ann["type"] = AnnType.topic
diff --git a/tests/data/serialize/hfml/opf/P000003.opf/index.yml b/tests/data/serialize/hfml/opf/P000003.opf/index.yml
index d294868a..271b83c8 100644
--- a/tests/data/serialize/hfml/opf/P000003.opf/index.yml
+++ b/tests/data/serialize/hfml/opf/P000003.opf/index.yml
@@ -3,7 +3,7 @@ annotation_type: index
 revision: '00001'
 annotations:
   12590fb37da14c32ba0785f7f68c6f5e:
-    parts: []
+    parts: {}
     span:
     - vol: 1
       start: 0
@@ -13,7 +13,7 @@ annotations:
       end: 218
     work_id: D1118
   ac26bb9b4a034a0fa959ecc6af68fa0e:
-    parts: []
+    parts: {}
     span:
     - vol: 2
       start: 218