diff --git a/flink-yarn/src/main/java/org/apache/flink/yarn/FlinkYarnCluster.java b/flink-yarn/src/main/java/org/apache/flink/yarn/FlinkYarnCluster.java
index 8d6b453cf4e4c..804b2e1109575 100644
--- a/flink-yarn/src/main/java/org/apache/flink/yarn/FlinkYarnCluster.java
+++ b/flink-yarn/src/main/java/org/apache/flink/yarn/FlinkYarnCluster.java
@@ -402,7 +402,7 @@ public static class PollingThread extends Thread {
 		private ApplicationId appId;
 
 		// ------- status information stored in the polling thread
-		private Object lock = new Object();
+		private final Object lock = new Object();
 		private ApplicationReport lastReport;