diff --git a/packages/cells/src/widget.ts b/packages/cells/src/widget.ts
index 76fc97d5465d..af4b212cc274 100644
--- a/packages/cells/src/widget.ts
+++ b/packages/cells/src/widget.ts
@@ -154,7 +154,7 @@ const RENDER_TIMEOUT = 1000;
 /**
  * The mime type for attachments
  */
-const ATTACHMENTS_MIME = 'application/vnd.jupyter.attachments';
+const ATTACHMENTS_MIME = 'application/vnd.jupyter.attachments;closure=true';
 
 /******************************************************************************
  * Cell
diff --git a/packages/filebrowser/src/listing.ts b/packages/filebrowser/src/listing.ts
index 8f1a25f65f8e..07f9c1dd848c 100644
--- a/packages/filebrowser/src/listing.ts
+++ b/packages/filebrowser/src/listing.ts
@@ -119,7 +119,7 @@ const CONTENTS_MIME = 'application/x-jupyter-icontents';
 /**
  * The mime type for attachments
  */
-const ATTACHMENTS_MIME = 'application/vnd.jupyter.attachments';
+const ATTACHMENTS_MIME = 'application/vnd.jupyter.attachments;closure=true';
 
 /**
  * The class name added to drop targets.