diff --git a/docs/manual/CoreTasks/jar.html b/docs/manual/CoreTasks/jar.html
index c4f88c1df..f37786b41 100644
--- a/docs/manual/CoreTasks/jar.html
+++ b/docs/manual/CoreTasks/jar.html
@@ -228,6 +228,14 @@ to a value other than its default, <code>"add"</code>.</b></p>
     (maximum compression/slowest). <em>Since Ant 1.7</em></td>
     <td valign="top" align="center">No</td>
   </tr>
+  <tr>
+    <td valign="top">strict</td>
+    <td valign="top">When this attribut is set to <tt>true</tt>, a BuildException 
+    will be thrown if the packaging version specification was broken. If set to 
+    <tt>false</tt> (default) only a message is logged (verbose).
+     <br>Defaults to false.  <em>Since Ant 1.7.1</em></td>
+    <td valign="top" align="center">No</td>
+  </tr>
 </table>
 
 <h3>Nested elements</h3>
diff --git a/src/etc/testcases/taskdefs/jar.xml b/src/etc/testcases/taskdefs/jar.xml
index 1f12bcc56..6b232e4d0 100644
--- a/src/etc/testcases/taskdefs/jar.xml
+++ b/src/etc/testcases/taskdefs/jar.xml
@@ -238,6 +238,11 @@
   </target>
     
   <target name="testNoVersionInfo">
+    <mkdir dir="${tmp.dir}"/>
+    <jar destfile="${tmp.jar}" basedir="${tmp.dir}" strict="true"/>
+  </target>  
+
+  <target name="testNoVersionInfoNoStrict">
     <mkdir dir="${tmp.dir}"/>
     <jar destfile="${tmp.jar}" basedir="${tmp.dir}"/>
   </target>  
@@ -245,7 +250,7 @@
   <!-- see http://java.sun.com/j2se/1.3/docs/guide/versioning/spec/VersioningSpecification.html#PackageVersioning -->  
   <target name="testHasVersionInfo">
     <mkdir dir="${tmp.dir}"/>
-    <jar destfile="${tmp.jar}" basedir="${tmp.dir}">
+    <jar destfile="${tmp.jar}" basedir="${tmp.dir}" strict="true">
       <manifest>
         <attribute name="Implementation-Title"   value="Packaging Version Test"/>
         <attribute name="Implementation-Version" value="1.0"/>
diff --git a/src/main/org/apache/tools/ant/taskdefs/Jar.java b/src/main/org/apache/tools/ant/taskdefs/Jar.java
index e3c6e3d29..de218d51f 100644
--- a/src/main/org/apache/tools/ant/taskdefs/Jar.java
+++ b/src/main/org/apache/tools/ant/taskdefs/Jar.java
@@ -143,6 +143,12 @@ public class Jar extends Zip {
      */
     private Path indexJars;
 
+    /**
+     * Strict mode for checking rules of the JAR-Specification.
+     * @see http://java.sun.com/j2se/1.3/docs/guide/versioning/spec/VersioningSpecification.html#PackageVersioning
+     */
+    private boolean strict = false;
+
     /**
      * Extra fields needed to make Solaris recognize the archive as a jar file.
      *
@@ -160,7 +166,7 @@ public class Jar extends Zip {
         setEncoding("UTF8");
         rootEntries = new Vector();
     }
-    
+
     /**
      * Not used for jar files.
      * @param we not used
@@ -185,6 +191,15 @@ public class Jar extends Zip {
         emptyBehavior = we.getValue();
     }
 
+    /**
+     * Activate the strict mode. When set to <i>true</i> a BuildException
+     * will be thrown if the Jar-Packaging specification was broken.
+     * @param strict New value of the strict mode.
+     */
+    public void setStrict(boolean strict) {
+        this.strict = strict;
+    }
+
     /**
      * Set the destination file.
      * @param jarFile the destination file
@@ -775,34 +790,55 @@ public class Jar extends Zip {
      */
     protected void cleanUp() {
         super.cleanUp();
-        
-        // check against packaging spec
-        // http://java.sun.com/j2se/1.3/docs/guide/versioning/spec/VersioningSpecification.html#PackageVersioning
-        Section mainSection = (configuredManifest==null) ? null : configuredManifest.getMainSection();
-        if (mainSection==null) {
-            log("No Implementation-Title set. (" + getLocation() + ")");
-            log("No Implementation-Version set. (" + getLocation() + ")");
-            log("No Implementation-Vendor set. (" + getLocation() + ")");
+        checkJarSpec();
+
+        // we want to save this info if we are going to make another pass
+        if (!doubleFilePass || !skipWriting) {
+            manifest = null;
+            configuredManifest = savedConfiguredManifest;
+            filesetManifest = null;
+            originalManifest = null;
+        }
+        rootEntries.removeAllElements();
+    }
+
+    /**
+     * Check against packaging spec
+     * @see http://java.sun.com/j2se/1.3/docs/guide/versioning/spec/VersioningSpecification.html#PackageVersioning
+     */
+    private void checkJarSpec() {
+        String br = System.getProperty("line.separator");
+        StringBuffer message = new StringBuffer();
+        Section mainSection = (configuredManifest == null)
+                            ? null 
+                            : configuredManifest.getMainSection();
+
+        if (mainSection == null) {
+            message.append("No Implementation-Title set.");
+            message.append("No Implementation-Version set.");
+            message.append("No Implementation-Vendor set.");
         } else {
             if (mainSection.getAttribute("Implementation-Title") == null) {
-                log("No Implementation-Title set. (" + getLocation() + ")");
+                message.append("No Implementation-Title set.");
             }
             if (mainSection.getAttribute("Implementation-Version") == null) {
-                log("No Implementation-Version set. (" + getLocation() + ")");
+                message.append("No Implementation-Version set.");
             }
             if (mainSection.getAttribute("Implementation-Vendor") == null) {
-                log("No Implementation-Vendor set. (" + getLocation() + ")");
+                message.append("No Implementation-Vendor set.");
             }
         }
 
-        // we want to save this info if we are going to make another pass
-        if (!doubleFilePass || !skipWriting) {
-            manifest = null;
-            configuredManifest = savedConfiguredManifest;
-            filesetManifest = null;
-            originalManifest = null;
+        if (message.length() > 0) {
+            message.append(br);
+            message.append("Location: ").append(getLocation());
+            message.append(br);
+            if (strict) {
+                throw new BuildException(message.toString(), getLocation());
+            } else {
+                log(message.toString(), Project.MSG_VERBOSE);
+            }
         }
-        rootEntries.removeAllElements();
     }
 
     /**
diff --git a/src/tests/junit/org/apache/tools/ant/taskdefs/JarTest.java b/src/tests/junit/org/apache/tools/ant/taskdefs/JarTest.java
index f5ad7092c..11766387a 100644
--- a/src/tests/junit/org/apache/tools/ant/taskdefs/JarTest.java
+++ b/src/tests/junit/org/apache/tools/ant/taskdefs/JarTest.java
@@ -269,12 +269,16 @@ public class JarTest extends BuildFileTest {
     }
     
     public void testNoVersionInfo() {
-        executeTarget("testNoVersionInfo");
-        assertLogContaining("No Implementation-Title set.");
-        assertLogContaining("No Implementation-Version set.");
-        assertLogContaining("No Implementation-Vendor set.");
+        expectBuildExceptionContaining("testNoVersionInfo", "Manifest Implemention information missing.", "No Implementation-Title set.");
     }
 
+    public void testNoVersionInfoNoStrict() {
+        executeTarget("testNoVersionInfoNoStrict");
+        assertFalse( getLog().contains("No Implementation-Title set.") );
+        assertFalse( getLog().contains("No Implementation-Version set.") );
+        assertFalse( getLog().contains("No Implementation-Vendor set.") );
+    }
+    
     public void testHasVersionInfo() {
         executeTarget("testHasVersionInfo");
         assertFalse( getLog().contains("No Implementation-Title set.") );