diff --git a/src/ArrayUtils.js b/src/ArrayUtils.js
new file mode 100644
index 0000000000..850fcc40f9
--- /dev/null
+++ b/src/ArrayUtils.js
@@ -0,0 +1,29 @@
+/*
+Copyright 2018 New Vector
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+/**
+ * creates a new array with only the unique values of the given array
+ * @return {array} the deduplicated array
+ */
+export function unique(arr) {
+    const cpy = [];
+    arr.forEach((el) => {
+        if (!cpy.includes(el)) {
+            cpy.push(el);
+        }
+    });
+    return cpy;
+};
diff --git a/src/utils/DMRoomMap.js b/src/utils/DMRoomMap.js
index 56832a1a75..cb76610e4d 100644
--- a/src/utils/DMRoomMap.js
+++ b/src/utils/DMRoomMap.js
@@ -15,6 +15,7 @@ limitations under the License.
 */
 
 import MatrixClientPeg from '../MatrixClientPeg';
+import {unique} from '../ArrayUtils';
 
 /**
  * Class that takes a Matrix Client and flips the m.direct map
@@ -120,19 +121,14 @@ export default class DMRoomMap {
                 return !guessedUserIdsThatChanged
                     .some((ids) => ids.roomId === roomId);
             });
-
             guessedUserIdsThatChanged.forEach(({userId, roomId}) => {
-                if (!userId) {
-                    // if not able to guess the other user (unlikely)
-                    // still put it in the map so the room stays marked
-                    // as a DM, we just wont be able to show an avatar.
-                    userId = "";
-                }
                 let roomIds = userToRooms[userId];
                 if (!roomIds) {
-                    roomIds = userToRooms[userId] = [];
+                    userToRooms[userId] = [roomId];
+                } else {
+                    roomIds.push(roomId);
+                    userToRooms[userId] = unique(roomIds);
                 }
-                roomIds.push(roomId);
             });
             return true;
         }