diff --git a/hadoop-common-project/hadoop-common/CHANGES.txt b/hadoop-common-project/hadoop-common/CHANGES.txt
index 583f6ae01e1..3a87612eb51 100644
--- a/hadoop-common-project/hadoop-common/CHANGES.txt
+++ b/hadoop-common-project/hadoop-common/CHANGES.txt
@@ -329,6 +329,8 @@ Release 2.6.0 - 2014-11-18
 
     HADOOP-11247. Fix a couple javac warnings in NFS. (Brandon Li via wheat9)
 
+    HADOOP-10786. Fix UGI#reloginFromKeytab on Java 8. (Stephen Chu via wheat9)
+
   BUG FIXES
 
     HADOOP-11182. GraphiteSink emits wrong timestamps (Sascha Coenen via raviprak)
diff --git a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/security/UserGroupInformation.java b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/security/UserGroupInformation.java
index fbefdb128a1..7fb036c06d5 100644
--- a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/security/UserGroupInformation.java
+++ b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/security/UserGroupInformation.java
@@ -86,9 +86,21 @@ public class UserGroupInformation {
    * Percentage of the ticket window to use before we renew ticket.
    */
   private static final float TICKET_RENEW_WINDOW = 0.80f;
+  private static boolean shouldRenewImmediatelyForTests = false;
   static final String HADOOP_USER_NAME = "HADOOP_USER_NAME";
   static final String HADOOP_PROXY_USER = "HADOOP_PROXY_USER";
-  
+
+  /**
+   * For the purposes of unit tests, we want to test login
+   * from keytab and don't want to wait until the renew
+   * window (controlled by TICKET_RENEW_WINDOW).
+   * @param immediate true if we should login without waiting for ticket window
+   */
+  @VisibleForTesting
+  static void setShouldRenewImmediatelyForTests(boolean immediate) {
+    shouldRenewImmediatelyForTests = immediate;
+  }
+
   /** 
    * UgiMetrics maintains UGI activity statistics
    * and publishes them through the metrics interfaces.
@@ -586,6 +598,20 @@ public class UserGroupInformation {
     user.setLogin(login);
   }
 
+  private static Class<?> KEY_TAB_CLASS = KerberosKey.class;
+  static {
+    try {
+      // We use KEY_TAB_CLASS to determine if the UGI is logged in from
+      // keytab. In JDK6 and JDK7, if useKeyTab and storeKey are specified
+      // in the Krb5LoginModule, then some number of KerberosKey objects
+      // are added to the Subject's private credentials. However, in JDK8,
+      // a KeyTab object is added instead. More details in HADOOP-10786.
+      KEY_TAB_CLASS = Class.forName("javax.security.auth.kerberos.KeyTab");
+    } catch (ClassNotFoundException cnfe) {
+      // Ignore. javax.security.auth.kerberos.KeyTab does not exist in JDK6.
+    }
+  }
+
   /**
    * Create a UserGroupInformation for the given subject.
    * This does not change the subject or acquire new credentials.
@@ -594,7 +620,7 @@ public class UserGroupInformation {
   UserGroupInformation(Subject subject) {
     this.subject = subject;
     this.user = subject.getPrincipals(User.class).iterator().next();
-    this.isKeytab = !subject.getPrivateCredentials(KerberosKey.class).isEmpty();
+    this.isKeytab = !subject.getPrivateCredentials(KEY_TAB_CLASS).isEmpty();
     this.isKrbTkt = !subject.getPrivateCredentials(KerberosTicket.class).isEmpty();
   }
   
@@ -950,7 +976,8 @@ public class UserGroupInformation {
         || !isKeytab)
       return;
     KerberosTicket tgt = getTGT();
-    if (tgt != null && Time.now() < getRefreshTime(tgt)) {
+    if (tgt != null && !shouldRenewImmediatelyForTests &&
+        Time.now() < getRefreshTime(tgt)) {
       return;
     }
     reloginFromKeytab();
@@ -975,13 +1002,14 @@ public class UserGroupInformation {
       return;
     
     long now = Time.now();
-    if (!hasSufficientTimeElapsed(now)) {
+    if (!shouldRenewImmediatelyForTests && !hasSufficientTimeElapsed(now)) {
       return;
     }
 
     KerberosTicket tgt = getTGT();
     //Return if TGT is valid and is not going to expire soon.
-    if (tgt != null && now < getRefreshTime(tgt)) {
+    if (tgt != null && !shouldRenewImmediatelyForTests &&
+        now < getRefreshTime(tgt)) {
       return;
     }
     
diff --git a/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/security/TestUGILoginFromKeytab.java b/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/security/TestUGILoginFromKeytab.java
new file mode 100644
index 00000000000..61fbf89178c
--- /dev/null
+++ b/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/security/TestUGILoginFromKeytab.java
@@ -0,0 +1,91 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.hadoop.security;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.fs.CommonConfigurationKeys;
+import org.apache.hadoop.minikdc.MiniKdc;
+import org.junit.After;
+import org.junit.Assert;
+import org.junit.Before;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.TemporaryFolder;
+
+import java.io.File;
+
+/**
+ * Verify UGI login from keytab. Check that the UGI is
+ * configured to use keytab to catch regressions like
+ * HADOOP-10786.
+ */
+public class TestUGILoginFromKeytab {
+
+  private MiniKdc kdc;
+  private File workDir;
+
+  @Rule
+  public final TemporaryFolder folder = new TemporaryFolder();
+
+  @Before
+  public void startMiniKdc() throws Exception {
+    // This setting below is required. If not enabled, UGI will abort
+    // any attempt to loginUserFromKeytab.
+    Configuration conf = new Configuration();
+    conf.set(CommonConfigurationKeys.HADOOP_SECURITY_AUTHENTICATION,
+        "kerberos");
+    UserGroupInformation.setConfiguration(conf);
+    workDir = folder.getRoot();
+    kdc = new MiniKdc(MiniKdc.createConf(), workDir);
+    kdc.start();
+  }
+
+  @After
+  public void stopMiniKdc() {
+    if (kdc != null) {
+      kdc.stop();
+    }
+  }
+
+  /**
+   * Login from keytab using the MiniKDC and verify the UGI can successfully
+   * relogin from keytab as well. This will catch regressions like HADOOP-10786.
+   */
+  @Test
+  public void testUGILoginFromKeytab() throws Exception {
+    UserGroupInformation.setShouldRenewImmediatelyForTests(true);
+    String principal = "foo";
+    File keytab = new File(workDir, "foo.keytab");
+    kdc.createPrincipal(keytab, principal);
+
+    UserGroupInformation.loginUserFromKeytab(principal, keytab.getPath());
+    UserGroupInformation ugi = UserGroupInformation.getLoginUser();
+    Assert.assertTrue("UGI should be configured to login from keytab",
+        ugi.isFromKeytab());
+
+    // Verify relogin from keytab.
+    User user = ugi.getSubject().getPrincipals(User.class).iterator().next();
+    final long firstLogin = user.getLastLogin();
+    ugi.reloginFromKeytab();
+    final long secondLogin = user.getLastLogin();
+    Assert.assertTrue("User should have been able to relogin from keytab",
+        secondLogin > firstLogin);
+  }
+
+}