diff --git a/enferno/admin/views/media.py b/enferno/admin/views/media.py
index 22c5554ba..14af3e33b 100644
--- a/enferno/admin/views/media.py
+++ b/enferno/admin/views/media.py
@@ -130,8 +130,10 @@ def api_medias_chunk() -> Response:
     """
     file = request.files["file"]
 
-    # Check if upload is from the media import tool (Admin-only extended extensions)
-    import_upload = request.form.get("source") == "import"
+    # Check if upload is from the media import tool (Admin-only extended extensions).
+    # The source param lives in the query string because Dropzone drops `params`
+    # on chunked POSTs, so a form-body check returns None on every chunk.
+    import_upload = request.args.get("source") == "import"
     # validate file extensions based on user and source
     if import_upload:
         # uploads from media import tool
diff --git a/enferno/data_import/templates/media-import.html b/enferno/data_import/templates/media-import.html
index ccded6dc3..530407448 100644
--- a/enferno/data_import/templates/media-import.html
+++ b/enferno/data_import/templates/media-import.html
@@ -377,7 +377,9 @@
                 batch_id: '',
 
                 dzOpts: {
-                    url: '/admin/api/media/chunk',
+                    // source=import goes in the URL so it survives every chunk POST.
+                    // Dropzone's `params` option is dropped on chunked requests.
+                    url: '/admin/api/media/chunk?source=import',
                     // accept any file
                     acceptedFiles: document.querySelector('[data-allowed-media-types]').dataset.allowedMediaTypes,
                     addRemoveLinks: true,
@@ -388,9 +390,6 @@
                     thumbnailHeight: 80,
                     parallelUploads: 1,
                     maxFilesize: mediaUploadMaxFileSize,
-                    // Signals the chunk endpoint to apply the Admin-only
-                    // extended extension list (ETL_VID_EXT).
-                    params: { source: 'import' },
                 },