diff --git a/event/relations.go b/event/relations.go
index e855a7e6..2316cbc7 100644
--- a/event/relations.go
+++ b/event/relations.go
@@ -34,7 +34,7 @@ type RelatesTo struct {
 type InReplyTo struct {
 	EventID id.EventID `json:"event_id,omitempty"`
 
-	UnstableRoomID id.RoomID `json:"room_id,omitempty"`
+	UnstableRoomID id.RoomID `json:"com.beeper.cross_room_id,omitempty"`
 }
 
 func (rel *RelatesTo) Copy() *RelatesTo {