diff --git a/src/components/structures/RoomView.js b/src/components/structures/RoomView.js
index 180e6ebc89..cfa4038114 100644
--- a/src/components/structures/RoomView.js
+++ b/src/components/structures/RoomView.js
@@ -183,6 +183,8 @@ module.exports = React.createClass({
         }
 
         this.setState(newState, () => {
+            // At this point, this.state.roomId could be null (e.g. the alias might not
+            // have been resolved yet) so anything called here must handle this case.
             this._onHaveRoom();
             this.onRoom(MatrixClientPeg.get().getRoom(this.state.roomId));
         });