diff --git a/hadoop-hdfs-project/hadoop-hdfs-httpfs/src/main/java/org/apache/hadoop/fs/http/server/HttpFSParametersProvider.java b/hadoop-hdfs-project/hadoop-hdfs-httpfs/src/main/java/org/apache/hadoop/fs/http/server/HttpFSParametersProvider.java
index 51752b63319..b2a28053da7 100644
--- a/hadoop-hdfs-project/hadoop-hdfs-httpfs/src/main/java/org/apache/hadoop/fs/http/server/HttpFSParametersProvider.java
+++ b/hadoop-hdfs-project/hadoop-hdfs-httpfs/src/main/java/org/apache/hadoop/fs/http/server/HttpFSParametersProvider.java
@@ -261,7 +261,7 @@ public class HttpFSParametersProvider extends ParametersProvider {
     /**
      * Parameter name.
      */
-    public static final String NAME = "len";
+    public static final String NAME = "length";
 
     /**
      * Constructor.
diff --git a/hadoop-hdfs-project/hadoop-hdfs-httpfs/src/test/java/org/apache/hadoop/fs/http/server/TestHttpFSServer.java b/hadoop-hdfs-project/hadoop-hdfs-httpfs/src/test/java/org/apache/hadoop/fs/http/server/TestHttpFSServer.java
index 910eeefb93e..6057a480214 100644
--- a/hadoop-hdfs-project/hadoop-hdfs-httpfs/src/test/java/org/apache/hadoop/fs/http/server/TestHttpFSServer.java
+++ b/hadoop-hdfs-project/hadoop-hdfs-httpfs/src/test/java/org/apache/hadoop/fs/http/server/TestHttpFSServer.java
@@ -24,6 +24,7 @@ import java.io.File;
 import java.io.FileOutputStream;
 import java.io.FileWriter;
 import java.io.IOException;
+import java.io.InputStream;
 import java.io.InputStreamReader;
 import java.io.OutputStream;
 import java.io.Writer;
@@ -146,6 +147,7 @@ public class TestHttpFSServer extends HFSTestCase {
     conf.set("httpfs.proxyuser." + HadoopUsersConfTestHelper.getHadoopProxyUser() + ".hosts",
              HadoopUsersConfTestHelper.getHadoopProxyUserHosts());
     conf.set("httpfs.authentication.signature.secret.file", secretFile.getAbsolutePath());
+    conf.set("httpfs.hadoop.config.dir", hadoopConfDir.toString());
     File httpfsSite = new File(new File(homeDir, "conf"), "httpfs-site.xml");
     os = new FileOutputStream(httpfsSite);
     conf.writeXml(os);
@@ -229,6 +231,31 @@ public class TestHttpFSServer extends HFSTestCase {
     reader.close();
   }
 
+  @Test
+  @TestDir
+  @TestJetty
+  @TestHdfs
+  public void testOpenOffsetLength() throws Exception {
+    createHttpFSServer(false);
+
+    byte[] array = new byte[]{0, 1, 2, 3};
+    FileSystem fs = FileSystem.get(TestHdfsHelper.getHdfsConf());
+    fs.mkdirs(new Path("/tmp"));
+    OutputStream os = fs.create(new Path("/tmp/foo"));
+    os.write(array);
+    os.close();
+
+    String user = HadoopUsersConfTestHelper.getHadoopUsers()[0];
+    URL url = new URL(TestJettyHelper.getJettyURL(),
+                      MessageFormat.format("/webhdfs/v1/tmp/foo?user.name={0}&op=open&offset=1&length=2", user));
+    HttpURLConnection conn = (HttpURLConnection) url.openConnection();
+    Assert.assertEquals(HttpURLConnection.HTTP_OK, conn.getResponseCode());
+    InputStream is = conn.getInputStream();
+    Assert.assertEquals(1, is.read());
+    Assert.assertEquals(2, is.read());
+    Assert.assertEquals(-1, is.read());
+  }
+
   @Test
   @TestDir
   @TestJetty
diff --git a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
index 645ff731fb1..5dc3b6ed409 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
+++ b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
@@ -64,6 +64,8 @@ Release 2.0.3-alpha - Unreleased
     HDFS-4000. TestParallelLocalRead fails with "input ByteBuffers
     must be direct buffers". (Colin Patrick McCabe via eli)
 
+    HDFS-3999. HttpFS OPEN operation expects len parameter, it should be length. (tucu)
+
 Release 2.0.2-alpha - 2012-09-07 
   
   INCOMPATIBLE CHANGES