diff --git a/lib/models/friend.dart b/lib/models/friend.dart
index c26799e..0a2599e 100644
--- a/lib/models/friend.dart
+++ b/lib/models/friend.dart
@@ -2,7 +2,7 @@ import 'package:contacts_plus_plus/models/session.dart';
 import 'package:contacts_plus_plus/models/user_profile.dart';
 import 'package:flutter/material.dart';
 
-class Friend extends Comparable {
+class Friend implements Comparable {
   final String id;
   final String username;
   final String ownerId;
diff --git a/lib/models/message.dart b/lib/models/message.dart
index 10f5314..fbc8c58 100644
--- a/lib/models/message.dart
+++ b/lib/models/message.dart
@@ -37,7 +37,7 @@ enum MessageState {
   read,
 }
 
-class Message extends Comparable {
+class Message implements Comparable {
   final String id;
   final String recipientId;
   final String senderId;