diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/BlockManager.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/BlockManager.java
index 0f6d6dd09ea..703200be350 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/BlockManager.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/BlockManager.java
@@ -2073,9 +2073,9 @@ void rescanPostponedMisreplicatedBlocks() {
       return;
     }
     long startTimeRescanPostponedMisReplicatedBlocks = Time.monotonicNow();
+    namesystem.writeLock();
     long startPostponedMisReplicatedBlocksCount =
         getPostponedMisreplicatedBlocksCount();
-    namesystem.writeLock();
     try {
       // blocksPerRescan is the configured number of blocks per rescan.
       // Randomly select blocksPerRescan consecutive blocks from the HashSet
@@ -2128,9 +2128,9 @@ void rescanPostponedMisreplicatedBlocks() {
         }
       }
     } finally {
-      namesystem.writeUnlock();
       long endPostponedMisReplicatedBlocksCount =
           getPostponedMisreplicatedBlocksCount();
+      namesystem.writeUnlock();
       LOG.info("Rescan of postponedMisreplicatedBlocks completed in " +
           (Time.monotonicNow() - startTimeRescanPostponedMisReplicatedBlocks) +
           " msecs. " + endPostponedMisReplicatedBlocksCount +