diff --git a/flink-runtime/src/main/java/org/apache/flink/runtime/leaderelection/ZooKeeperLeaderElectionService.java b/flink-runtime/src/main/java/org/apache/flink/runtime/leaderelection/ZooKeeperLeaderElectionService.java
index d1fd548f742cc20463333f9bbd78822b410742e5..709d0319faab8e565e2d51efd3dd46e94e608b4f 100644
--- a/flink-runtime/src/main/java/org/apache/flink/runtime/leaderelection/ZooKeeperLeaderElectionService.java
+++ b/flink-runtime/src/main/java/org/apache/flink/runtime/leaderelection/ZooKeeperLeaderElectionService.java
@@ -114,8 +114,10 @@ public class ZooKeeperLeaderElectionService implements LeaderElectionService, Le
 		leaderLatch.close();
 		client.close();
 
-		confirmedLeaderSessionID = null;
-		issuedLeaderSessionID = null;
+		synchronized (lock) {
+			confirmedLeaderSessionID = null;
+			issuedLeaderSessionID = null;
+		}
 	}
 
 	@Override