diff --git a/README.md b/README.md
index b88c23076..9936f93d1 100644
--- a/README.md
+++ b/README.md
@@ -8,27 +8,27 @@
 [![Dependency Status](https://www.versioneye.com/php/silverstripe:framework/badge.svg)](https://www.versioneye.com/php/silverstripe:framework)
 [![Reference Status](https://www.versioneye.com/php/silverstripe:framework/reference_badge.svg?style=flat)](https://www.versioneye.com/php/silverstripe:framework/references)
 
-PHP5 framework forming the base for the SilverStripe CMS ([http://silverstripe.org](http://silverstripe.org)). 
-Requires a [`silverstripe-installer`](http://github.com/silverstripe/silverstripe-installer) base project. Typically used alongside the [`cms`](http://github.com/silverstripe/silverstripe-cms) module.
+PHP5 framework forming the base for the SilverStripe CMS ([https://silverstripe.org](https://silverstripe.org)). 
+Requires a [`silverstripe-installer`](https://github.com/silverstripe/silverstripe-installer) base project. Typically used alongside the [`cms`](https://github.com/silverstripe/silverstripe-cms) module.
 
 ## Installation ##
 
-See [installation on different platforms](http://doc.silverstripe.org/framework/en/installation/),
-and [installation from source](http://doc.silverstripe.org/framework/en/installation/from-source).
+See [installation on different platforms](https://doc.silverstripe.org/framework/en/installation/),
+and [installation from source](https://doc.silverstripe.org/framework/en/installation/from-source).
 
 ## Bugtracker ##
 
 Bugs are tracked on [github.com](https://github.com/silverstripe/silverstripe-framework/issues). 
-Please read our [issue reporting guidelines](http://doc.silverstripe.org/framework/en/misc/contributing/issues).
+Please read our [issue reporting guidelines](https://doc.silverstripe.org/framework/en/misc/contributing/issues).
 
 ## Development and Contribution ##
 
-If you would like to make changes to the SilverStripe core codebase, we have an extensive [guide to contributing code](http://doc.silverstripe.org/framework/en/misc/contributing/code).
+If you would like to make changes to the SilverStripe core codebase, we have an extensive [guide to contributing code](https://docs.silverstripe.org/en/contributing/code/).
 
 ## Links ##
 
- * [Server Requirements](http://doc.silverstripe.org/framework/en/installation/server-requirements)
- * [Changelogs](http://doc.silverstripe.org/framework/en/changelogs/)
+ * [Server Requirements](https://doc.silverstripe.org/framework/en/installation/server-requirements)
+ * [Changelogs](https://doc.silverstripe.org/framework/en/changelogs/)
  * [Bugtracker: Framework](https://github.com/silverstripe/silverstripe-framework/issues)
  * [Bugtracker: CMS](https://github.com/silverstripe/silverstripe-cms/issues)
  * [Bugtracker: Installer](https://github.com/silverstripe/silverstripe-installer/issues)
diff --git a/model/DataObject.php b/model/DataObject.php
index 6be82cc4a..50acf1e8a 100644
--- a/model/DataObject.php
+++ b/model/DataObject.php
@@ -586,7 +586,20 @@ class DataObject extends ViewableData implements DataObjectInterface, i18nEntity
 	private function duplicateRelations($sourceObject, $destinationObject, $name) {
 		$relations = $sourceObject->$name();
 		if ($relations) {
-			if ($relations instanceOf RelationList) {   //many-to-something relation
+            if ($relations instanceOf ManyManyList) { //many-to-many relation
+                $extraFieldNames = $relations->getExtraFields();
+
+                if ($relations->Count() > 0) {  //with more than one thing it is related to
+					foreach($relations as $relation) {
+                        // Merge extra fields
+                        $extraFields = array();
+                        foreach ($extraFieldNames as $fieldName => $fieldType) {
+                            $extraFields[$fieldName] = $relation->getField($fieldName);
+                        }
+                        $destinationObject->$name()->add($relation, $extraFields);
+                    }
+                }
+            } else if ($relations instanceOf RelationList) {   //many-to-something relation
 				if ($relations->Count() > 0) {  //with more than one thing it is related to
 					foreach($relations as $relation) {
 						$destinationObject->$name()->add($relation);
diff --git a/tests/model/DataObjectDuplicationTest.php b/tests/model/DataObjectDuplicationTest.php
index e3b24fece..2fcab1c4d 100644
--- a/tests/model/DataObjectDuplicationTest.php
+++ b/tests/model/DataObjectDuplicationTest.php
@@ -77,7 +77,7 @@ class DataObjectDuplicationTest extends SapphireTest {
 
 		//create relations
 		$one->twos()->add($two);
-		$one->threes()->add($three);
+		$one->threes()->add($three, array('TestExtra'=>'three'));
 
 		$one = DataObject::get_by_id("DataObjectDuplicateTestClass1", $one->ID);
 		$two = DataObject::get_by_id("DataObjectDuplicateTestClass2", $two->ID);
@@ -115,6 +115,9 @@ class DataObjectDuplicationTest extends SapphireTest {
 			"Match between relation of copy and the original");
 		$this->assertEquals($one->ID, $threeCopy->ones()->First()->ID,
 			"Match between relation of copy and the original");
+
+		$this->assertEquals('three', $oneCopy->threes()->First()->TestExtra,
+			"Match between extra field of copy and the original");
 	}
 
 }
@@ -133,6 +136,12 @@ class DataObjectDuplicateTestClass1 extends DataObject implements TestOnly {
 	private static $many_many = array(
 		'threes' => 'DataObjectDuplicateTestClass3'
 	);
+
+	private static $many_many_extraFields = array(
+		'threes' => array(
+            'TestExtra' => 'Varchar'
+        )
+	);
 }
 
 class DataObjectDuplicateTestClass2 extends DataObject implements TestOnly {