diff --git a/app/src/main/java/com/vitorpamplona/amethyst/model/Note.kt b/app/src/main/java/com/vitorpamplona/amethyst/model/Note.kt
index 4b63c8547..d8f633116 100644
--- a/app/src/main/java/com/vitorpamplona/amethyst/model/Note.kt
+++ b/app/src/main/java/com/vitorpamplona/amethyst/model/Note.kt
@@ -155,6 +155,7 @@ open class Note(val idHex: String) {
         }
     }
 
+    @Synchronized
     fun addZap(zapRequest: Note, zap: Note?) {
         if (zapRequest !in zaps.keys) {
             zaps = zaps + Pair(zapRequest, zap)