diff --git a/src/drc/api/serializers/bestandsdeel.py b/src/drc/api/serializers/bestandsdeel.py
index 12c3c6b3..10054de7 100644
--- a/src/drc/api/serializers/bestandsdeel.py
+++ b/src/drc/api/serializers/bestandsdeel.py
@@ -7,8 +7,6 @@
 
 class BestandsDeelSerializer(serializers.HyperlinkedModelSerializer):
     lock = serializers.CharField(
-        read_only=True,
-        source="canonical.lock",
         help_text="Hash string, which represents id of the lock of related informatieobject",
     )
 
diff --git a/src/drc/api/serializers/enkelvoudig_informatieobject.py b/src/drc/api/serializers/enkelvoudig_informatieobject.py
index 4d17de29..689e88fd 100644
--- a/src/drc/api/serializers/enkelvoudig_informatieobject.py
+++ b/src/drc/api/serializers/enkelvoudig_informatieobject.py
@@ -238,7 +238,7 @@ def _create_bestandsdeel(self, full_size, canonical):
         for i in range(parts):
             chunk_size = min(settings.CHUNK_SIZE, full_size)
             BestandsDeel.objects.create(
-                informatieobject=canonical, omvang=chunk_size, volgnummer=i + 1
+                informatieobject=canonical, omvang=chunk_size, volgnummer=i + 1, lock=canonical.lock
             )
             full_size -= chunk_size
 
@@ -266,10 +266,6 @@ def create(self, validated_data):
         eio.ondertekening = ondertekening
         eio.save()
 
-        # large file process
-        if not eio.inhoud and eio.bestandsomvang and eio.bestandsomvang > 0:
-            self._create_bestandsdeel(validated_data["bestandsomvang"], canonical)
-
         # create empty file if size == 0
         if eio.bestandsomvang == 0:
             eio.inhoud.save("empty_file", ContentFile(""))
@@ -381,6 +377,8 @@ def create(self, validated_data):
         # lock document if it is a large file upload
         if not eio.inhoud and eio.bestandsomvang and eio.bestandsomvang > 0:
             eio.canonical.lock = uuid.uuid4().hex
+            # large file process
+            self._create_bestandsdeel(validated_data["bestandsomvang"], eio.canonical)
             eio.canonical.save()
         return eio