diff --git a/src/main/java/net/openhft/chronicle/threads/EventGroup.java b/src/main/java/net/openhft/chronicle/threads/EventGroup.java
index 8bf997ab4..eaeff8dfe 100755
--- a/src/main/java/net/openhft/chronicle/threads/EventGroup.java
+++ b/src/main/java/net/openhft/chronicle/threads/EventGroup.java
@@ -78,9 +78,11 @@ public void addHandler(@NotNull EventHandler handler) {
 
     @Override
     public void start() {
-        core.start();
-        monitor.start();
-        monitor.addHandler(new LoopBlockMonitor());
+        if (!core.isAlive()) {
+            core.start();
+            monitor.start();
+            monitor.addHandler(new LoopBlockMonitor());
+        }
     }
 
     @Override