diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2f370f7c..2809e430 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -15,6 +15,7 @@ and this project adheres to
 ### Fixed
 
 - ✨(frontend) sync backend user language to browser on load
+- 🐛(backend) fix WOPI PutFile to check stored file size
 
 ## [v0.13.0] - 2026-02-18
 
diff --git a/src/backend/wopi/tests/viewset/test_put_file_content.py b/src/backend/wopi/tests/viewset/test_put_file_content.py
index 9228baab..0ebd4e9c 100644
--- a/src/backend/wopi/tests/viewset/test_put_file_content.py
+++ b/src/backend/wopi/tests/viewset/test_put_file_content.py
@@ -352,6 +352,7 @@ def test_put_file_content_with_no_lock_header_and_body_size_greater_than_0():
         update_upload_state=models.ItemUploadStateChoices.READY,
         link_reach=models.LinkReachChoices.RESTRICTED,
         link_role=models.LinkRoleChoices.EDITOR,
+        size=100,
     )
     user = factories.UserFactory()
     factories.UserItemAccessFactory(
@@ -374,7 +375,8 @@ def test_put_file_content_with_no_lock_header_and_body_size_greater_than_0():
     assert response.headers.get("X-WOPI-Lock") == ""
 
 
-def test_put_file_content_with_no_lock_header_and_body_size_0():
+@pytest.mark.parametrize("data", [b"", b"new content"])
+def test_put_file_content_with_no_lock_header_and_body_size_0(data):
     """User can put file content when not providing a lock header and the body size is 0."""
     folder = factories.ItemFactory(
         type=models.ItemTypeChoices.FOLDER,
@@ -386,6 +388,7 @@ def test_put_file_content_with_no_lock_header_and_body_size_0():
         update_upload_state=models.ItemUploadStateChoices.READY,
         link_reach=models.LinkReachChoices.RESTRICTED,
         link_role=models.LinkRoleChoices.EDITOR,
+        size=0,
     )
     user = factories.UserFactory()
     factories.UserItemAccessFactory(
@@ -397,7 +400,7 @@ def test_put_file_content_with_no_lock_header_and_body_size_0():
     client = APIClient()
     response = client.post(
         f"/api/v1.0/wopi/files/{item.id}/contents/",
-        data=b"",
+        data=data,
         content_type="text/plain",
         HTTP_AUTHORIZATION=f"Bearer {access_token}",
         headers={
@@ -413,5 +416,5 @@ def test_put_file_content_with_no_lock_header_and_body_size_0():
         Bucket=default_storage.bucket_name,
         Key=item.file_key,
     )
-    assert file["Body"].read() == b""
+    assert file["Body"].read() == data
     assert response.headers.get("X-WOPI-ItemVersion") == file["VersionId"]
diff --git a/src/backend/wopi/viewsets.py b/src/backend/wopi/viewsets.py
index 3263f31e..f94a6054 100644
--- a/src/backend/wopi/viewsets.py
+++ b/src/backend/wopi/viewsets.py
@@ -143,7 +143,6 @@ class WopiViewSet(viewsets.ViewSet):
         Implementation of the Wopi PutFile file operation
         https://learn.microsoft.com/en-us/microsoft-365/cloud-storage-partner-program/rest/files/putfile
         """
-
         if request.META.get(HTTP_X_WOPI_OVERRIDE) != "PUT":
             return Response(status=404)
 
@@ -154,7 +153,6 @@ class WopiViewSet(viewsets.ViewSet):
             return Response(status=401)
 
         lock_value = request.META.get(HTTP_X_WOPI_LOCK)
-
         if lock_value:
             lock_service = LockService(item)
             current_lock_value = lock_service.get_lock(default="")
@@ -162,7 +160,7 @@ class WopiViewSet(viewsets.ViewSet):
                 return Response(status=409, headers={X_WOPI_LOCK: current_lock_value})
         else:
             # Check if the body is 0 bytes
-            body_size = int(request.META.get("CONTENT_LENGTH") or 0)
+            body_size = item.size or 0
             if body_size > 0:
                 return Response(status=409, headers={X_WOPI_LOCK: ""})