diff --git a/lib/Doctrine/ORM/UnderscoreNamingStrategy.php b/lib/Doctrine/ORM/UnderscoreNamingStrategy.php
index 409b4f0ee..b00b15990 100644
--- a/lib/Doctrine/ORM/UnderscoreNamingStrategy.php
+++ b/lib/Doctrine/ORM/UnderscoreNamingStrategy.php
@@ -19,7 +19,6 @@
  */
 
 namespace Doctrine\ORM;
-use Doctrine\Common\Util\Inflector;
 
 /**
  * The default NamingStrategy
@@ -122,12 +121,12 @@ class UnderscoreNamingStrategy implements NamingStrategy
      */
     private function underscore($string)
     {
-        $string = Inflector::tableize($string);
+        $string = preg_replace('/(?<=[a-z])([A-Z])/', '_$1', $string);
 
         if ($this->case == self::CASE_UPPER) {
             return strtoupper($string);
         }
         
-        return $string;
+        return strtolower($string);
     }
 }
\ No newline at end of file
diff --git a/tests/Doctrine/Tests/ORM/Mapping/ClassMetadataTest.php b/tests/Doctrine/Tests/ORM/Mapping/ClassMetadataTest.php
index 7a4de4ca4..da591238d 100644
--- a/tests/Doctrine/Tests/ORM/Mapping/ClassMetadataTest.php
+++ b/tests/Doctrine/Tests/ORM/Mapping/ClassMetadataTest.php
@@ -293,6 +293,51 @@ class ClassMetadataTest extends \Doctrine\Tests\OrmTestCase
         $this->assertEquals('cmsuser_id', $cm->associationMappings['user']['joinTable']['inverseJoinColumns'][0]['name']);
     }
 
+    /**
+     * @group DDC-559
+     */
+    public function testUnderscoreNamingStrategyDefaults()
+    {
+        $namingStrategy     = new \Doctrine\ORM\UnderscoreNamingStrategy(\Doctrine\ORM\UnderscoreNamingStrategy::CASE_UPPER);
+        $oneToOneMetadata   = new ClassMetadata('Doctrine\Tests\Models\CMS\CmsAddress', $namingStrategy);
+        $manyToManyMetadata = new ClassMetadata('Doctrine\Tests\Models\CMS\CmsAddress', $namingStrategy);
+
+        $oneToOneMetadata->mapOneToOne(array(
+            'fieldName'     => 'user',
+            'targetEntity'  => 'CmsUser'
+        ));
+
+        $manyToManyMetadata->mapManyToMany(array(
+            'fieldName'     => 'user',
+            'targetEntity'  => 'CmsUser'
+        ));
+        
+        $this->assertEquals(array('USER_ID'=>'ID'), $oneToOneMetadata->associationMappings['user']['sourceToTargetKeyColumns']);
+        $this->assertEquals(array('USER_ID'=>'USER_ID'), $oneToOneMetadata->associationMappings['user']['joinColumnFieldNames']);
+        $this->assertEquals(array('ID'=>'USER_ID'), $oneToOneMetadata->associationMappings['user']['targetToSourceKeyColumns']);
+
+        $this->assertEquals('USER_ID', $oneToOneMetadata->associationMappings['user']['joinColumns'][0]['name']);
+        $this->assertEquals('ID', $oneToOneMetadata->associationMappings['user']['joinColumns'][0]['referencedColumnName']);
+
+        
+        $this->assertEquals('CMS_ADDRESS_CMS_USER', $manyToManyMetadata->associationMappings['user']['joinTable']['name']);
+
+        $this->assertEquals(array('CMS_ADDRESS_ID','CMS_USER_ID'), $manyToManyMetadata->associationMappings['user']['joinTableColumns']);
+        $this->assertEquals(array('CMS_ADDRESS_ID'=>'ID'), $manyToManyMetadata->associationMappings['user']['relationToSourceKeyColumns']);
+        $this->assertEquals(array('CMS_USER_ID'=>'ID'), $manyToManyMetadata->associationMappings['user']['relationToTargetKeyColumns']);
+
+        $this->assertEquals('CMS_ADDRESS_ID', $manyToManyMetadata->associationMappings['user']['joinTable']['joinColumns'][0]['name']);
+        $this->assertEquals('CMS_USER_ID', $manyToManyMetadata->associationMappings['user']['joinTable']['inverseJoinColumns'][0]['name']);
+
+        $this->assertEquals('ID', $manyToManyMetadata->associationMappings['user']['joinTable']['joinColumns'][0]['referencedColumnName']);
+        $this->assertEquals('ID', $manyToManyMetadata->associationMappings['user']['joinTable']['inverseJoinColumns'][0]['referencedColumnName']);
+
+
+        $cm = new ClassMetadata('DoctrineGlobal_Article', $namingStrategy);
+        $cm->mapManyToMany(array('fieldName' => 'author', 'targetEntity' => 'Doctrine\Tests\Models\CMS\CmsUser'));
+        $this->assertEquals('DOCTRINE_GLOBAL_ARTICLE_CMS_USER', $cm->associationMappings['author']['joinTable']['name']);
+    }
+
     /**
      * @group DDC-886
      */
diff --git a/tests/Doctrine/Tests/ORM/NamingStrategyTest.php b/tests/Doctrine/Tests/ORM/NamingStrategyTest.php
index bf4ab7254..354ea67ff 100644
--- a/tests/Doctrine/Tests/ORM/NamingStrategyTest.php
+++ b/tests/Doctrine/Tests/ORM/NamingStrategyTest.php
@@ -106,6 +106,12 @@ class NamingStrategyTest extends \Doctrine\Tests\OrmTestCase
             array(self::underscoreNamingUpper(), 'SOME_PROPERTY',
                 'someProperty'
             ),
+            array(self::underscoreNamingUpper(), 'SOME_PROPERTY',
+                'some_property'
+            ),
+            array(self::underscoreNamingUpper(), 'SOME_PROPERTY',
+                'SOME_PROPERTY'
+            ),
         );
     }