diff --git a/services/storage/src/simcore_service_storage/models.py b/services/storage/src/simcore_service_storage/models.py
index bc4c9d8b9e6..2e21fc2483c 100644
--- a/services/storage/src/simcore_service_storage/models.py
+++ b/services/storage/src/simcore_service_storage/models.py
@@ -1,7 +1,7 @@
 import datetime
 import urllib.parse
 from dataclasses import dataclass
-from typing import Literal, NamedTuple, Self
+from typing import Any, Literal, NamedTuple
 from uuid import UUID
 
 import arrow
@@ -186,14 +186,18 @@ def convert_from_lower_case(cls, v: str) -> str:
             return f"{v}".upper()
         return v
 
-    @model_validator(mode="after")
-    def when_directory_force_link_type_and_file_size(self) -> Self:
-        if self.is_directory is True:
+    @model_validator(mode="before")
+    @classmethod
+    def when_directory_force_link_type_and_file_size(cls, data: Any) -> Any:
+        assert isinstance(data, dict)
+
+        if bool(data.get("is_directory", False)) is True:
             # sets directory size by default to undefined
-            self.file_size = None
+            if int(data.get("file_size", -1)) < 0:
+                data["file_size"] = None
             # only 1 link will be returned manged by the uploader
-            self.link_type = LinkType.S3
-        return self
+            data["link_type"] = LinkType.S3.value
+        return data
 
     @property
     def is_v1_upload(self) -> bool:
diff --git a/services/storage/tests/unit/test_handlers_files.py b/services/storage/tests/unit/test_handlers_files.py
index 88da46df3ad..16e56f7b170 100644
--- a/services/storage/tests/unit/test_handlers_files.py
+++ b/services/storage/tests/unit/test_handlers_files.py
@@ -1199,8 +1199,8 @@ async def test_copy_as_soft_link(
 
     # now let's try with whatever link id
     file, original_file_uuid = await upload_file(
-        TypeAdapter(ByteSize, "10Mib")
-    ).validate_python(faker.file_name())
+        TypeAdapter(ByteSize).validate_python("10Mib"), faker.file_name()
+    )
     url = (
         client.app.router["copy_as_soft_link"]
         .url_for(
@@ -1208,7 +1208,9 @@ async def test_copy_as_soft_link(
         )
         .with_query(user_id=user_id)
     )
-    link_id = SimcoreS3FileID(f"api/{node_id}/{faker.file_name()}")
+    link_id = TypeAdapter(SimcoreS3FileID).validate_python(
+        f"api/{node_id}/{faker.file_name()}"
+    )
     response = await client.post(
         f"{url}", json=jsonable_encoder(SoftCopyBody(link_id=link_id))
     )
@@ -1442,12 +1444,12 @@ async def test_listing_with_project_id_filter(
     project, src_projects_list = await random_project_with_files(
         num_nodes=1,
         file_sizes=(ByteSize(1),),
-        file_checksums=(SHA256Str(faker.sha256()),),
+        file_checksums=(TypeAdapter(SHA256Str).validate_python(faker.sha256()),),
     )
     _, _ = await random_project_with_files(
         num_nodes=1,
         file_sizes=(ByteSize(1),),
-        file_checksums=(SHA256Str(faker.sha256()),),
+        file_checksums=(TypeAdapter(SHA256Str).validate_python(faker.sha256()),),
     )
     assert len(src_projects_list.keys()) > 0
     node_id = next(iter(src_projects_list.keys()))