diff --git a/bioimageio_collection_backoffice/generate_collection_json.py b/bioimageio_collection_backoffice/generate_collection_json.py
index 88a84156..fc5662b3 100644
--- a/bioimageio_collection_backoffice/generate_collection_json.py
+++ b/bioimageio_collection_backoffice/generate_collection_json.py
@@ -80,7 +80,10 @@ def maybe_swap_with_thumbnail(
 
         if isinstance(src, str):
             clean_name = Path(src).name  # remove any leading './'
-            return thumbnails.get(clean_name, src)
+            if clean_name in thumbnails:
+                return p.get_file_url(thumbnails[clean_name])
+            else:
+                return src
 
         return src
 
diff --git a/bioimageio_collection_backoffice/remote_resource.py b/bioimageio_collection_backoffice/remote_resource.py
index 64e021a7..19528ec1 100644
--- a/bioimageio_collection_backoffice/remote_resource.py
+++ b/bioimageio_collection_backoffice/remote_resource.py
@@ -255,6 +255,9 @@ def get_uploader(self):
 
         return Uploader(email=email, name=name)
 
+    def get_file_url(self, path: str):
+        return self.client.get_file_url(f"{self.folder}files/{path}")
+
     def get_file_urls(self):
         return self.client.get_file_urls(f"{self.folder}files/")