diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSDirAttrOp.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSDirAttrOp.java
index 1dbee96985c..6da59eda09f 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSDirAttrOp.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSDirAttrOp.java
@@ -332,38 +332,35 @@ public class FSDirAttrOp {
 
     INodeDirectory dirNode =
         INodeDirectory.valueOf(iip.getLastINode(), iip.getPath());
+    final QuotaCounts oldQuota = dirNode.getQuotaCounts();
+    final long oldNsQuota = oldQuota.getNameSpace();
+    final long oldSsQuota = oldQuota.getStorageSpace();
     if (dirNode.isRoot() && nsQuota == HdfsConstants.QUOTA_RESET) {
-      throw new IllegalArgumentException("Cannot clear namespace quota on root.");
-    } else { // a directory inode
-      final QuotaCounts oldQuota = dirNode.getQuotaCounts();
-      final long oldNsQuota = oldQuota.getNameSpace();
-      final long oldSsQuota = oldQuota.getStorageSpace();
+      nsQuota = HdfsConstants.QUOTA_DONT_SET;
+    } else if (nsQuota == HdfsConstants.QUOTA_DONT_SET) {
+      nsQuota = oldNsQuota;
+    } // a directory inode
+    if (ssQuota == HdfsConstants.QUOTA_DONT_SET) {
+      ssQuota = oldSsQuota;
+    }
 
-      if (nsQuota == HdfsConstants.QUOTA_DONT_SET) {
-        nsQuota = oldNsQuota;
-      }
-      if (ssQuota == HdfsConstants.QUOTA_DONT_SET) {
-        ssQuota = oldSsQuota;
-      }
+    // unchanged space/namespace quota
+    if (type == null && oldNsQuota == nsQuota && oldSsQuota == ssQuota) {
+      return null;
+    }
 
-      // unchanged space/namespace quota
-      if (type == null && oldNsQuota == nsQuota && oldSsQuota == ssQuota) {
+    // unchanged type quota
+    if (type != null) {
+      EnumCounters<StorageType> oldTypeQuotas = oldQuota.getTypeSpaces();
+      if (oldTypeQuotas != null && oldTypeQuotas.get(type) == ssQuota) {
         return null;
       }
-
-      // unchanged type quota
-      if (type != null) {
-          EnumCounters<StorageType> oldTypeQuotas = oldQuota.getTypeSpaces();
-          if (oldTypeQuotas != null && oldTypeQuotas.get(type) == ssQuota) {
-              return null;
-          }
-      }
-
-      final int latest = iip.getLatestSnapshotId();
-      dirNode.recordModification(latest);
-      dirNode.setQuota(fsd.getBlockStoragePolicySuite(), nsQuota, ssQuota, type);
-      return dirNode;
     }
+
+    final int latest = iip.getLatestSnapshotId();
+    dirNode.recordModification(latest);
+    dirNode.setQuota(fsd.getBlockStoragePolicySuite(), nsQuota, ssQuota, type);
+    return dirNode;
   }
 
   static BlockInfo[] unprotectedSetReplication(
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/TestQuota.java b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/TestQuota.java
index 1c4855fc701..f5d232c0a6b 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/TestQuota.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/TestQuota.java
@@ -413,13 +413,13 @@ public class TestQuota {
       }
     });
 
-    // 19: clrQuota on the root directory ("/") should fail
-    runCommand(admin, true, "-clrQuota", "/");
+    // 19: clrQuota on the root directory ("/") should pass.
+    runCommand(admin, false, "-clrQuota", "/");
 
     // 20: setQuota on the root directory ("/") should succeed
     runCommand(admin, false, "-setQuota", "1000000", "/");
 
-    runCommand(admin, true, "-clrQuota", "/");
+    runCommand(admin, false, "-clrQuota", "/");
     runCommand(admin, false, "-clrSpaceQuota", "/");
     runCommand(admin, new String[]{"-clrQuota", parent.toString()}, false);
     runCommand(admin, false, "-clrSpaceQuota", parent.toString());
@@ -456,7 +456,7 @@ public class TestQuota {
     final Path childFile4 = new Path(dir, "datafile2");
     final Path childFile5 = new Path(dir, "datafile3");
 
-    runCommand(admin, true, "-clrQuota", "/");
+    runCommand(admin, false, "-clrQuota", "/");
     runCommand(admin, false, "-clrSpaceQuota", "/");
     // set space quota to a real low value
     runCommand(admin, false, "-setSpaceQuota", Long.toString(spaceQuota2), "/");
@@ -1565,6 +1565,19 @@ public class TestQuota {
     assertEquals(0, cluster.getNamesystem().getNumFilesUnderConstruction());
   }
 
+  @Test
+  public void testClrQuotaOnRoot() throws Exception {
+    long orignalQuota = dfs.getQuotaUsage(new Path("/")).getQuota();
+    DFSAdmin admin = new DFSAdmin(conf);
+    String[] args;
+    args = new String[] {"-setQuota", "3K", "/"};
+    runCommand(admin, args, false);
+    assertEquals(3 * 1024, dfs.getQuotaUsage(new Path("/")).getQuota());
+    args = new String[] {"-clrQuota", "/"};
+    runCommand(admin, args, false);
+    assertEquals(orignalQuota, dfs.getQuotaUsage(new Path("/")).getQuota());
+  }
+
   @Test
   public void testSpaceQuotaExceptionOnAppend() throws Exception {
     GenericTestUtils.setLogLevel(DFSOutputStream.LOG, Level.TRACE);