diff --git a/hadoop-mapreduce-project/CHANGES.txt b/hadoop-mapreduce-project/CHANGES.txt
index da0e8e10337..83811654e0b 100644
--- a/hadoop-mapreduce-project/CHANGES.txt
+++ b/hadoop-mapreduce-project/CHANGES.txt
@@ -98,8 +98,11 @@ Release 0.23.2 - UNRELEASED
   OPTIMIZATIONS
 
   BUG FIXES
-  MAPREDUCE-3840.  JobEndNotifier doesn't use the proxyToUse during connecting
-  (Ravi Prakash via bobby)
+    MAPREDUCE-3680. FifoScheduler web service rest API can print out invalid 
+    JSON. (B Anil Kumar via tgraves)
+
+    MAPREDUCE-3840.  JobEndNotifier doesn't use the proxyToUse during connecting
+    (Ravi Prakash via bobby)
 
 Release 0.23.1 - 2012-02-08 
 
diff --git a/hadoop-mapreduce-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/fifo/FifoScheduler.java b/hadoop-mapreduce-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/fifo/FifoScheduler.java
index 3d904f3a8c2..6fcf1fedd9d 100644
--- a/hadoop-mapreduce-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/fifo/FifoScheduler.java
+++ b/hadoop-mapreduce-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/fifo/FifoScheduler.java
@@ -148,7 +148,12 @@ public QueueInfo getQueueInfo(
       QueueInfo queueInfo = recordFactory.newRecordInstance(QueueInfo.class);
       queueInfo.setQueueName(DEFAULT_QUEUE.getQueueName());
       queueInfo.setCapacity(1.0f);
-      queueInfo.setCurrentCapacity((float)usedResource.getMemory() / clusterResource.getMemory());
+      if (clusterResource.getMemory() == 0) {
+        queueInfo.setCurrentCapacity(0.0f);
+      } else {
+        queueInfo.setCurrentCapacity((float) usedResource.getMemory()
+            / clusterResource.getMemory());
+      }
       queueInfo.setMaximumCapacity(1.0f);
       queueInfo.setChildQueues(new ArrayList<QueueInfo>());
       queueInfo.setQueueState(QueueState.RUNNING);
diff --git a/hadoop-mapreduce-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/test/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/fifo/TestFifoScheduler.java b/hadoop-mapreduce-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/test/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/fifo/TestFifoScheduler.java
index a50d4c21700..88e6e63e17b 100644
--- a/hadoop-mapreduce-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/test/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/fifo/TestFifoScheduler.java
+++ b/hadoop-mapreduce-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/test/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/fifo/TestFifoScheduler.java
@@ -29,6 +29,7 @@
 import org.apache.hadoop.yarn.api.records.ApplicationAttemptId;
 import org.apache.hadoop.yarn.api.records.ApplicationId;
 import org.apache.hadoop.yarn.api.records.Priority;
+import org.apache.hadoop.yarn.api.records.QueueInfo;
 import org.apache.hadoop.yarn.api.records.Resource;
 import org.apache.hadoop.yarn.event.AsyncDispatcher;
 import org.apache.hadoop.yarn.server.resourcemanager.Application;
@@ -74,6 +75,13 @@ public void tearDown() throws Exception {
             .getRMContext());
   }
   
+  @Test
+  public void testFifoSchedulerCapacityWhenNoNMs() {
+    FifoScheduler scheduler = new FifoScheduler();
+    QueueInfo queueInfo = scheduler.getQueueInfo(null, false, false);
+    Assert.assertEquals(0.0f, queueInfo.getCurrentCapacity());
+  }
+  
   @Test
   public void testAppAttemptMetrics() throws Exception {
     AsyncDispatcher dispatcher = new InlineDispatcher();
diff --git a/hadoop-mapreduce-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/test/java/org/apache/hadoop/yarn/server/resourcemanager/webapp/TestRMWebServices.java b/hadoop-mapreduce-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/test/java/org/apache/hadoop/yarn/server/resourcemanager/webapp/TestRMWebServices.java
index fc73c0251a4..bf0df460ac9 100644
--- a/hadoop-mapreduce-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/test/java/org/apache/hadoop/yarn/server/resourcemanager/webapp/TestRMWebServices.java
+++ b/hadoop-mapreduce-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/test/java/org/apache/hadoop/yarn/server/resourcemanager/webapp/TestRMWebServices.java
@@ -539,7 +539,7 @@ public void verifyClusterSchedulerFifoGeneric(String type, String state,
     assertEquals("type doesn't match", "fifoScheduler", type);
     assertEquals("qstate doesn't match", QueueState.RUNNING.toString(), state);
     assertEquals("capacity doesn't match", 1.0, capacity, 0.0);
-    assertEquals("usedCapacity doesn't match", Float.NaN, usedCapacity, 0.0);
+    assertEquals("usedCapacity doesn't match", 0.0, usedCapacity, 0.0);
     assertEquals("minQueueMemoryCapacity doesn't match", 1024, minQueueCapacity);
     assertEquals("maxQueueMemoryCapacity doesn't match", 10240,
         maxQueueCapacity);