diff --git a/WHATSNEW b/WHATSNEW
index 31b0ed743..1ee15e205 100644
--- a/WHATSNEW
+++ b/WHATSNEW
@@ -39,6 +39,10 @@ Changes that could break older environments:
   defined in the project.  If you rely on the task waiting for input,
   don't use the addproperty attribute.
 
+* The Class-Path attribute in manifests will no longer merge the
+  entries of all manifests found, but will be treated like all other
+  manifest attributes - the most recent attribute(s) will be used.
+
 Fixed bugs:
 -----------
 * Filter readers were not handling line endings properly.  Bugzilla
@@ -182,6 +186,9 @@ Fixed bugs:
 * Nested websphere element for ejbjar does not support spaces in file name.
   Bugzilla Report 21298
 
+* Don't multiply Class-Path attributes when updating jars.  Bugzilla
+  Report 21170.
+
 Other changes:
 --------------
 * Six new Clearcase tasks added.
diff --git a/src/main/org/apache/tools/ant/taskdefs/Manifest.java b/src/main/org/apache/tools/ant/taskdefs/Manifest.java
index 6f9dcc3ea..703c1f46f 100644
--- a/src/main/org/apache/tools/ant/taskdefs/Manifest.java
+++ b/src/main/org/apache/tools/ant/taskdefs/Manifest.java
@@ -459,16 +459,19 @@ public class Manifest {
             }
 
             Enumeration e = section.getAttributeKeys();
+            Attribute classpathAttribute = null;
             while (e.hasMoreElements()) {
                 String attributeName = (String) e.nextElement();
                 Attribute attribute = section.getAttribute(attributeName);
-                if (attributeName.equals(ATTRIBUTE_CLASSPATH) &&
-                        attributes.containsKey(attributeName)) {
-                    Attribute ourClassPath = getAttribute(attributeName);
+                if (attributeName.equals(ATTRIBUTE_CLASSPATH)) {
+                    if (classpathAttribute == null) {
+                        classpathAttribute = new Attribute();
+                        classpathAttribute.setName(ATTRIBUTE_CLASSPATH);
+                    }
                     Enumeration cpe = attribute.getValues();
                     while (cpe.hasMoreElements()) {
                         String value = (String) cpe.nextElement();
-                        ourClassPath.addValue(value);
+                        classpathAttribute.addValue(value);
                     }
                 } else {
                     // the merge file always wins
@@ -476,6 +479,11 @@ public class Manifest {
                 }
             }
 
+            if (classpathAttribute != null) {
+                // the merge file *always* wins, even for Class-Path
+                storeAttribute(classpathAttribute);
+            }
+
             // add in the warnings
             Enumeration warnEnum = section.warnings.elements();
             while (warnEnum.hasMoreElements()) {