diff --git a/widget/public/MANIFEST b/widget/public/MANIFEST
index 7b5f1edfc3b3..84a9c85a8f27 100644
--- a/widget/public/MANIFEST
+++ b/widget/public/MANIFEST
@@ -9,6 +9,7 @@ nsIDataFlavor.h
 nsITransferable.h
 nsIGenericTransferable.h
 nsIDragService.h
+nsIDragSession.h
 nsui.h
 nsIWidget.h
 nsIButton.h