diff --git a/app/src/main/java/com/vitorpamplona/amethyst/model/User.kt b/app/src/main/java/com/vitorpamplona/amethyst/model/User.kt
index 396585f2b..ada5bdde8 100644
--- a/app/src/main/java/com/vitorpamplona/amethyst/model/User.kt
+++ b/app/src/main/java/com/vitorpamplona/amethyst/model/User.kt
@@ -189,6 +189,7 @@ class User(val pubkeyHex: String) {
         }
     }
 
+    @Synchronized
     fun addMessage(user: User, msg: Note) {
         val privateChatroom = getOrCreatePrivateChatroom(user)
         if (msg !in privateChatroom.roomMessages) {
@@ -197,6 +198,7 @@ class User(val pubkeyHex: String) {
         }
     }
 
+    @Synchronized
     fun removeMessage(user: User, msg: Note) {
         val privateChatroom = getOrCreatePrivateChatroom(user)
         if (msg in privateChatroom.roomMessages) {