diff --git a/pulsar-metadata/src/main/java/org/apache/pulsar/metadata/impl/ZKSessionWatcher.java b/pulsar-metadata/src/main/java/org/apache/pulsar/metadata/impl/ZKSessionWatcher.java
index a350d4a5b3..ed6870824b 100644
--- a/pulsar-metadata/src/main/java/org/apache/pulsar/metadata/impl/ZKSessionWatcher.java
+++ b/pulsar-metadata/src/main/java/org/apache/pulsar/metadata/impl/ZKSessionWatcher.java
@@ -80,7 +80,11 @@ public class ZKSessionWatcher implements AutoCloseable, Watcher {
     }
 
     // task that runs every TICK_TIME to check zk connection
-    private synchronized void checkConnectionStatus() {
+    // NOT ThreadSafe:
+    // If zk client can't ensure the order, it may lead to problems.
+    // Currently,we only use it in single thread, it will be fine. but we shouldn't leave any potential problems
+    // in the future.
+    private void checkConnectionStatus() {
         try {
             CompletableFuture<Watcher.Event.KeeperState> future = new CompletableFuture<>();
             zk.exists("/", false, (StatCallback) (rc, path, ctx, stat) -> {
@@ -125,7 +129,7 @@ public class ZKSessionWatcher implements AutoCloseable, Watcher {
         currentStatus = SessionEvent.SessionLost;
     }
 
-    private void checkState(Watcher.Event.KeeperState zkClientState) {
+    private synchronized void checkState(Watcher.Event.KeeperState zkClientState) {
         switch (zkClientState) {
         case Expired:
             if (currentStatus != SessionEvent.SessionLost) {