diff --git a/bus/src/main/java/de/srsoftware/umbrella/messagebus/MessageBus.java b/bus/src/main/java/de/srsoftware/umbrella/messagebus/MessageBus.java
index 75aca937..f5919e88 100644
--- a/bus/src/main/java/de/srsoftware/umbrella/messagebus/MessageBus.java
+++ b/bus/src/main/java/de/srsoftware/umbrella/messagebus/MessageBus.java
@@ -3,6 +3,8 @@ package de.srsoftware.umbrella.messagebus;
 
 import de.srsoftware.umbrella.messagebus.events.Event;
 import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
 import java.util.Set;
 
 public class MessageBus {
@@ -15,7 +17,7 @@ public class MessageBus {
 		new Thread(() -> { // TODO: use thread pool
 			try {
 				Thread.sleep(100);
-				listeners.parallelStream().forEach(l -> l.onEvent(event));
+				List.copyOf(listeners).parallelStream().forEach(l -> l.onEvent(event));
 			} catch (InterruptedException ignored) {
 			}
 		}).start();