diff --git a/ws2012/P2P/uebungen/4/src/node/Node.java b/ws2012/P2P/uebungen/4/src/node/Node.java
index 6cba241e..8f2ea031 100644
--- a/ws2012/P2P/uebungen/4/src/node/Node.java
+++ b/ws2012/P2P/uebungen/4/src/node/Node.java
@@ -196,7 +196,12 @@ public class Node {
 			sendLeave(neighbors.get(i));
 		}
 
-		try {
+        try {
+            // Wait until all we received all acks
+            while (!acks.isEmpty()) {
+                Thread.sleep(10);
+            }
+
 			if (thread != null) {
 				udpListen.terminate();
 				thread.join();
@@ -257,7 +262,7 @@ public class Node {
 				Ack theAck = acks.get(ack_id);
 				if (theAck.check(from)) {
 					theAck.setReceived();
-					acks.remove(theAck);
+                    acks.remove(theAck.getId());
 				}
 			}
 		}
@@ -270,7 +275,7 @@ public class Node {
 			if (idToRemove != -1) {
 				neighbors.remove(idToRemove);
 				int ack_id = buf.getInt();
-				sendAck(from, ack_id);
+                sendAck(from, ack_id);
 			}
 			// If we don't know that neighbor, we don't have to
 			// ack