diff --git a/joram/a3/rt/src/main/java/fr/dyade/aaa/agent/AgentServer.java b/joram/a3/rt/src/main/java/fr/dyade/aaa/agent/AgentServer.java
index f5ba60f7eb7b594c720afa941b87b239afb6cfa7..426202f80c59832bb8a58b43b9776b512c96d346 100644
--- a/joram/a3/rt/src/main/java/fr/dyade/aaa/agent/AgentServer.java
+++ b/joram/a3/rt/src/main/java/fr/dyade/aaa/agent/AgentServer.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2001 - 2020 ScalAgent Distributed Technologies
+ * Copyright (C) 2001 - 2021 ScalAgent Distributed Technologies
  * Copyright (C) 2004 France Telecom R&D
  * Copyright (C) 1996 - 2000 BULL
  * Copyright (C) 1996 - 2000 INRIA
@@ -461,6 +461,12 @@ public final class AgentServer {
     checkServerTask.registerListener(listener);
   }
   
+  public static void unregisterCheckServerListener(CheckServerListener listener) {
+    if (checkServerTask == null)
+      logmon.log(BasicLevel.ERROR, getName() + " cannot unregister CheckServerListener.");
+    checkServerTask.unregisterListener(listener);
+  }
+
   static ThreadGroup tgroup = null;
 
   public static ThreadGroup getThreadGroup() {
@@ -1923,13 +1929,19 @@ class CheckServerTask extends TimerTask {
     listeners = new Vector<CheckServerListener>();
   }
 
-  public void registerListener(CheckServerListener listener) {
+  public synchronized void registerListener(CheckServerListener listener) {
     logmon.log(BasicLevel.INFO,
                AgentServer.getName() + " registers listener for CheckServer.");
     listeners.addElement(listener);
   }
 
-  private void throwListeners() {
+  public synchronized void unregisterListener(CheckServerListener listener) {
+    logmon.log(BasicLevel.INFO,
+               AgentServer.getName() + " unregisters listener for CheckServer.");
+    listeners.removeElement(listener);
+  }
+
+  private synchronized void throwListeners() {
     for (CheckServerListener listener : listeners) {
       logmon.log(BasicLevel.DEBUG,
                  AgentServer.getName() + " calls listener for CheckServer.");
@@ -1974,8 +1986,8 @@ class CheckServerTask extends TimerTask {
     if (! engine.isRunning()) {
       // The engine does not run, just log a warn if needed
       if (((now - lastEngineChangeDate) > dtwarn) && ((now - lastEngineWarnDate) > dtwarn)) {
-        logmon.log(BasicLevel.DEBUG,
-                   AgentServer.getName() + ", engine is not started.");
+        logmon.log(BasicLevel.WARN,
+                   AgentServer.getName() + ", engine is not running.");
         lastEngineWarnDate = now;
       }
       return false;