Index: maven-core/src/main/java/org/apache/maven/plugin/MavenPluginDiscoverer.java
===================================================================
--- maven-core/src/main/java/org/apache/maven/plugin/MavenPluginDiscoverer.java	(revision 169072)
+++ maven-core/src/main/java/org/apache/maven/plugin/MavenPluginDiscoverer.java	(working copy)
@@ -47,6 +47,6 @@
     public ComponentSetDescriptor createComponentDescriptors( Reader componentDescriptorConfiguration, String source )
         throws PlexusConfigurationException
     {
-        return builder.build( componentDescriptorConfiguration );
+        return builder.build( componentDescriptorConfiguration, source );
     }
 }
Index: maven-plugin-descriptor/src/main/java/org/apache/maven/plugin/descriptor/PluginDescriptorBuilder.java
===================================================================
--- maven-plugin-descriptor/src/main/java/org/apache/maven/plugin/descriptor/PluginDescriptorBuilder.java	(revision 169072)
+++ maven-plugin-descriptor/src/main/java/org/apache/maven/plugin/descriptor/PluginDescriptorBuilder.java	(working copy)
@@ -19,13 +19,20 @@
  */
 public class PluginDescriptorBuilder
 {
-    public PluginDescriptor build( Reader reader )
+    public PluginDescriptor build( Reader reader )
         throws PlexusConfigurationException
     {
+        return build( reader, null );
+    }
+
+    public PluginDescriptor build( Reader reader, String source )
+        throws PlexusConfigurationException
+    {
         PlexusConfiguration c = buildConfiguration( reader );
 
         PluginDescriptor pluginDescriptor = new PluginDescriptor();
 
+        pluginDescriptor.setSource( source );
         pluginDescriptor.setGroupId( c.getChild( "groupId" ).getValue() );
         pluginDescriptor.setArtifactId( c.getChild( "artifactId" ).getValue() );
         pluginDescriptor.setVersion( c.getChild( "version" ).getValue() );
Index: maven-plugin-descriptor/src/main/java/org/apache/maven/plugin/descriptor/PluginDescriptor.java
===================================================================
--- maven-plugin-descriptor/src/main/java/org/apache/maven/plugin/descriptor/PluginDescriptor.java	(revision 169072)
+++ maven-plugin-descriptor/src/main/java/org/apache/maven/plugin/descriptor/PluginDescriptor.java	(working copy)
@@ -39,6 +39,8 @@
 
     private String goalPrefix;
 
+    private String source;
+
     // ----------------------------------------------------------------------
     //
     // ----------------------------------------------------------------------
@@ -109,7 +111,7 @@
         String id = constructPluginKey( groupId, artifactId, version );
         if ( groupId == null || artifactId == null || version == null )
         {
-            throw new IllegalStateException( "Plugin descriptor ID incomplete: " + id );
+            throw new IllegalStateException( "Plugin descriptor ID incomplete: " + id + " in " + getSource() );
         }
         return id;
     }
@@ -174,4 +176,14 @@
     {
         return version;
     }
+
+    public void setSource( String source )
+    {
+        this.source = source;
+    }
+
+    public String getSource()
+    {
+        return source;
+    }
 }