diff --git a/CHANGES.txt b/CHANGES.txt
index eec3971..9ab598d 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -100,6 +100,9 @@
     MAPREDUCE-2074. Task should fail when symlink creation fails.
     (Priyo Mustafi via tomwhite)
 
+    MAPREDUCE-1242. Chain APIs error misleading.
+    (Harsh J Chouraria via tomwhite)
+
 Release 0.22.0 - Unreleased
 
   INCOMPATIBLE CHANGES
diff --git a/src/java/org/apache/hadoop/mapreduce/lib/chain/Chain.java b/src/java/org/apache/hadoop/mapreduce/lib/chain/Chain.java
index 3441b7c..384524a 100644
--- a/src/java/org/apache/hadoop/mapreduce/lib/chain/Chain.java
+++ b/src/java/org/apache/hadoop/mapreduce/lib/chain/Chain.java
@@ -692,13 +692,13 @@
           + CHAIN_MAPPER_CONFIG + (index - 1));
       if (!inputKeyClass.isAssignableFrom(previousMapperConf.getClass(
           MAPPER_OUTPUT_KEY_CLASS, null))) {
-        throw new IllegalArgumentException("The Mapper output key class does"
-            + " not match the previous Mapper input key class");
+        throw new IllegalArgumentException("The specified Mapper input key class does"
+            + " not match the previous Mapper's output key class.");
       }
       if (!inputValueClass.isAssignableFrom(previousMapperConf.getClass(
           MAPPER_OUTPUT_VALUE_CLASS, null))) {
-        throw new IllegalArgumentException("The Mapper output value class"
-            + " does not match the previous Mapper input value class");
+        throw new IllegalArgumentException("The specified Mapper input value class"
+            + " does not match the previous Mapper's output value class.");
       }
     }
   }