diff --git a/event-schemas/schema/core-event-schema/msgtype_infos/thumbnail_info.yaml b/event-schemas/schema/core-event-schema/msgtype_infos/thumbnail_info.yaml
index 1daea3fc2..30ee4a240 100644
--- a/event-schemas/schema/core-event-schema/msgtype_infos/thumbnail_info.yaml
+++ b/event-schemas/schema/core-event-schema/msgtype_infos/thumbnail_info.yaml
@@ -14,3 +14,4 @@ properties:
     description: The width of the image in pixels.
     type: integer
 title: ThumbnailInfo
+type: object