diff --git a/hadoop-mapreduce-project/CHANGES.txt b/hadoop-mapreduce-project/CHANGES.txt
index 11e37eb4a0..1c4926f245 100644
--- a/hadoop-mapreduce-project/CHANGES.txt
+++ b/hadoop-mapreduce-project/CHANGES.txt
@@ -49,6 +49,8 @@ Trunk (unreleased changes)
     Move the support for multiple protocols to lower layer so that Writable,
     PB and Avro can all use it (Sanjay)
 
+    MAPREDUCE-2944. Improve checking of input for JobClient.displayTasks() (XieXianshan via harsh)
+
   BUG FIXES
     MAPREDUCE-3349. Log rack-name in JobHistory for unsuccessful tasks. 
                     (Devaraj K and Amar Kamat via amarrk)
diff --git a/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapred/JobClient.java b/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapred/JobClient.java
index fa3d799fe7..be9981a592 100644
--- a/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapred/JobClient.java
+++ b/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapred/JobClient.java
@@ -723,6 +723,8 @@ public TaskReport[] getReduceTaskReports(String jobId) throws IOException {
    * @param type the type of the task (map/reduce/setup/cleanup)
    * @param state the state of the task 
    * (pending/running/completed/failed/killed)
+   * @throws IOException when there is an error communicating with the master
+   * @throws IllegalArgumentException if an invalid type/state is passed
    */
   public void displayTasks(final JobID jobId, String type, String state) 
   throws IOException {
diff --git a/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapreduce/tools/CLI.java b/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapreduce/tools/CLI.java
index f7ac9c40a6..c42456aafc 100644
--- a/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapreduce/tools/CLI.java
+++ b/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapreduce/tools/CLI.java
@@ -20,6 +20,9 @@
 import java.io.IOException;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Set;
+import java.util.HashSet;
+import java.util.Arrays;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
@@ -56,6 +59,10 @@
 public class CLI extends Configured implements Tool {
   private static final Log LOG = LogFactory.getLog(CLI.class);
   protected Cluster cluster;
+  private final Set<String> taskTypes = new HashSet<String>(
+              Arrays.asList("map", "reduce", "setup", "cleanup"));
+  private final Set<String> taskStates = new HashSet<String>(
+              Arrays.asList("pending", "running", "completed", "failed", "killed"));
 
   public CLI() {
   }
@@ -545,9 +552,21 @@ private void printTaskAttempts(TaskReport report) {
    * @param type the type of the task (map/reduce/setup/cleanup)
    * @param state the state of the task 
    * (pending/running/completed/failed/killed)
+   * @throws IOException when there is an error communicating with the master
+   * @throws InterruptedException
+   * @throws IllegalArgumentException if an invalid type/state is passed
    */
   protected void displayTasks(Job job, String type, String state) 
   throws IOException, InterruptedException {
+    if (!taskTypes.contains(type)) {
+      throw new IllegalArgumentException("Invalid type: " + type + 
+          ". Valid types for task are: map, reduce, setup, cleanup.");
+    }
+    if (!taskStates.contains(state)) {
+      throw new java.lang.IllegalArgumentException("Invalid state: " + state + 
+          ". Valid states for task are: pending, running, completed, failed, killed.");
+    }
+
     TaskReport[] reports = job.getTaskReports(TaskType.valueOf(type));
     for (TaskReport report : reports) {
       TIPStatus status = report.getCurrentStatus();