diff --git a/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/DataStreamer.java b/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/DataStreamer.java
index 4fa578ab6c..d92f5943fd 100644
--- a/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/DataStreamer.java
+++ b/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/DataStreamer.java
@@ -476,6 +476,7 @@ boolean doWaitForRestart() {
   private DataOutputStream blockStream;
   private DataInputStream blockReplyStream;
   private ResponseProcessor response = null;
+  private final Object nodesLock = new Object();
   private volatile DatanodeInfo[] nodes = null; // list of targets for current block
   private volatile StorageType[] storageTypes = null;
   private volatile String[] storageIDs = null;
@@ -619,7 +620,9 @@ private void setPipeline(LocatedBlock lb) {
 
   private void setPipeline(DatanodeInfo[] nodes, StorageType[] storageTypes,
                            String[] storageIDs) {
-    this.nodes = nodes;
+    synchronized (nodesLock) {
+      this.nodes = nodes;
+    }
     this.storageTypes = storageTypes;
     this.storageIDs = storageIDs;
   }
@@ -916,7 +919,10 @@ void waitForAckedSeqno(long seqno) throws IOException {
     try (TraceScope ignored = dfsClient.getTracer().
         newScope("waitForAckedSeqno")) {
       LOG.debug("{} waiting for ack for: {}", this, seqno);
-      int dnodes = nodes != null ? nodes.length : 3;
+      int dnodes;
+      synchronized (nodesLock) {
+        dnodes = nodes != null ? nodes.length : 3;
+      }
       int writeTimeout = dfsClient.getDatanodeWriteTimeout(dnodes);
       long begin = Time.monotonicNow();
       try {