diff --git a/hadoop-mapreduce-project/CHANGES.txt b/hadoop-mapreduce-project/CHANGES.txt
index c90960ec839..8e766887c9a 100644
--- a/hadoop-mapreduce-project/CHANGES.txt
+++ b/hadoop-mapreduce-project/CHANGES.txt
@@ -58,6 +58,9 @@ Release 2.0.5-beta - UNRELEASED
     MAPREDUCE-4716. TestHsWebServicesJobsQuery.testJobsQueryStateInvalid 
     fails with jdk7. (tgraves via tucu)
 
+    MAPREDUCE-5028. Maps fail when io.sort.mb is set to high value. 
+    (kkambatl via tucu)
+
 Release 2.0.4-alpha - UNRELEASED
 
   INCOMPATIBLE CHANGES
diff --git a/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapred/MapTask.java b/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapred/MapTask.java
index cd4ba51c31c..496ca2e6565 100644
--- a/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapred/MapTask.java
+++ b/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapred/MapTask.java
@@ -1165,8 +1165,9 @@ public class MapTask extends Task {
       equator = pos;
       // set index prior to first entry, aligned at meta boundary
       final int aligned = pos - (pos % METASIZE);
-      kvindex =
-        ((aligned - METASIZE + kvbuffer.length) % kvbuffer.length) / 4;
+      // Cast one of the operands to long to ensure large values don't cause int
+      // overflow
+      kvindex = (int) (((long) aligned - METASIZE + kvbuffer.length) % kvbuffer.length) / 4;
       if (LOG.isInfoEnabled()) {
         LOG.info("(EQUATOR) " + pos + " kvi " + kvindex +
             "(" + (kvindex * 4) + ")");
@@ -1183,8 +1184,9 @@ public class MapTask extends Task {
       bufstart = bufend = e;
       final int aligned = e - (e % METASIZE);
       // set start/end to point to first meta record
-      kvstart = kvend =
-        ((aligned - METASIZE + kvbuffer.length) % kvbuffer.length) / 4;
+      // Cast one of the operands to long to ensure large values don't cause int
+      // overflow
+      kvstart = kvend = (int) (((long) aligned - METASIZE + kvbuffer.length) % kvbuffer.length) / 4;
       if (LOG.isInfoEnabled()) {
         LOG.info("(RESET) equator " + e + " kv " + kvstart + "(" +
           (kvstart * 4) + ")" + " kvi " + kvindex + "(" + (kvindex * 4) + ")");
@@ -1748,7 +1750,7 @@ public class MapTask extends Task {
           this.start = 0;
         }
 
-        super.reset(this.buffer, this.start, this.length);
+        super.reset(this.buffer, this.start, this.length - this.start);
       }
     }
 
diff --git a/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapreduce/task/ReduceContextImpl.java b/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapreduce/task/ReduceContextImpl.java
index 7ad08e956d9..8736de52f8c 100644
--- a/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapreduce/task/ReduceContextImpl.java
+++ b/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapreduce/task/ReduceContextImpl.java
@@ -205,7 +205,8 @@ public class ReduceContextImpl<KEYIN,VALUEIN,KEYOUT,VALUEOUT>
           if (backupStore.hasNext()) {
             backupStore.next();
             DataInputBuffer next = backupStore.nextValue();
-            buffer.reset(next.getData(), next.getPosition(), next.getLength());
+            buffer.reset(next.getData(), next.getPosition(), next.getLength()
+                - next.getPosition());
             value = valueDeserializer.deserialize(value);
             return value;
           } else {
diff --git a/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapreduce/task/reduce/InMemoryReader.java b/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapreduce/task/reduce/InMemoryReader.java
index 543ff3f9cc7..6def88b97b4 100644
--- a/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapreduce/task/reduce/InMemoryReader.java
+++ b/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapreduce/task/reduce/InMemoryReader.java
@@ -49,14 +49,14 @@ public class InMemoryReader<K, V> extends Reader<K, V> {
 
     buffer = data;
     bufferSize = (int)fileLength;
-    memDataIn.reset(buffer, start, length);
+    memDataIn.reset(buffer, start, length - start);
     this.start = start;
     this.length = length;
   }
 
   @Override
   public void reset(int offset) {
-    memDataIn.reset(buffer, start + offset, length);
+    memDataIn.reset(buffer, start + offset, length - start - offset);
     bytesRead = offset;
     eof = false;
   }