diff --git a/src/utils/DMRoomMap.js b/src/utils/DMRoomMap.js
index 0089ebbe5b..3bcc492a9f 100644
--- a/src/utils/DMRoomMap.js
+++ b/src/utils/DMRoomMap.js
@@ -32,7 +32,9 @@ export default class DMRoomMap {
     }
 
     getDMRoomsForUserId(userId) {
-        return this.userToRooms[userId];
+        // Here, we return the empty list if there are no rooms,
+        // since the number of conversations you have with this user is zero.
+        return this.userToRooms[userId] || [];
     }
 
     getUserIdForRoomId(roomId) {
@@ -45,6 +47,8 @@ export default class DMRoomMap {
             // is never called.
             this._populateRoomToUser();
         }
+        // Here, we return undefined if the room is not in the map:
+        // the room ID you gave is not a DM room for any user.
         return this.roomToUser[roomId];
     }