diff --git a/src/models/event.js b/src/models/event.js
index fb4e51068..6fd80750a 100644
--- a/src/models/event.js
+++ b/src/models/event.js
@@ -61,7 +61,9 @@ module.exports.EventStatus = {
  * from changes to event JSON between Matrix versions.
  *
  * @prop {RoomMember} sender The room member who sent this event, or null e.g.
- * this is a presence event.
+ * this is a presence event. This is only guarenteed to be set for events that
+ * appear in a timeline, ie. do not guarentee that it will be set on state
+ * events.
  * @prop {RoomMember} target The room member who is the target of this event, e.g.
  * the invitee, the person being banned, etc.
  * @prop {EventStatus} status The sending status of the event.