diff --git a/core/Core.php b/core/Core.php
index 04626150e..993011e3b 100644
--- a/core/Core.php
+++ b/core/Core.php
@@ -365,15 +365,10 @@ function getClassFile($className) {
  * @return Object
  */
 function singleton($className) {
-	global $_SINGLETONS;
+	if($className == "Config") user_error("Don't pass Config to singleton()", E_USER_ERROR);
 	if(!isset($className)) user_error("singleton() Called without a class", E_USER_ERROR);
 	if(!is_string($className)) user_error("singleton() passed bad class_name: " . var_export($className,true), E_USER_ERROR);
-	if(!isset($_SINGLETONS[$className])) {
-		if(!class_exists($className)) user_error("Bad class to singleton() - $className", E_USER_ERROR);
-		$_SINGLETONS[$className] = Injector::inst()->get($className);
-		if(!$_SINGLETONS[$className]) user_error("singleton() Unknown class '$className'", E_USER_ERROR);
-	}
-	return $_SINGLETONS[$className];
+	return Injector::inst()->get($className);
 }
 
 function project() {
diff --git a/core/Object.php b/core/Object.php
index 104f2f5e2..08e3d165d 100755
--- a/core/Object.php
+++ b/core/Object.php
@@ -466,6 +466,7 @@ abstract class Object {
 		}
 
 		Config::inst()->update($class, 'extensions', array($extension));
+		Injector::inst()->unregisterAllObjects();
 
 		// load statics now for DataObject classes
 		if(is_subclass_of($class, 'DataObject')) {
@@ -496,8 +497,7 @@ abstract class Object {
 		Config::inst()->remove($class, 'extensions', Config::anything(), $extension);
 
 		// unset singletons to avoid side-effects
-		global $_SINGLETONS;
-		$_SINGLETONS = array();
+		Injector::inst()->unregisterAllObjects();
 
 		// unset some caches
 		$subclasses = ClassInfo::subclassesFor($class);
@@ -541,7 +541,6 @@ abstract class Object {
 		
 		if($extensionClasses = ClassInfo::ancestry($this->class)) foreach($extensionClasses as $class) {
 			if(in_array($class, $notExtendable)) continue;
-
 			if($extensions = Config::inst()->get($class, 'extensions', Config::UNINHERITED)) {
 				foreach($extensions as $extension) {
 					// Get the extension class for this extension
diff --git a/dev/SapphireTest.php b/dev/SapphireTest.php
index 7216ab3fe..609a0d0f1 100644
--- a/dev/SapphireTest.php
+++ b/dev/SapphireTest.php
@@ -299,8 +299,7 @@ class SapphireTest extends PHPUnit_Framework_TestCase {
 		}
 		// clear singletons, they're caching old extension info 
 		// which is used in DatabaseAdmin->doBuild()
-		global $_SINGLETONS;
-		$_SINGLETONS = array();
+		Injector::inst()->unregisterAllObjects();
 
 		// Set default timezone consistently to avoid NZ-specific dependencies
 		date_default_timezone_set('UTC');
@@ -789,9 +788,7 @@ class SapphireTest extends PHPUnit_Framework_TestCase {
 	function resetDBSchema($includeExtraDataObjects = false) {
 		if(self::using_temp_db()) {
 			// clear singletons, they're caching old extension info which is used in DatabaseAdmin->doBuild()
-			global $_SINGLETONS;
 			Injector::inst()->unregisterAllObjects();
-			$_SINGLETONS = array();
 
 			$dataClasses = ClassInfo::subclassesFor('DataObject');
 			array_shift($dataClasses);
diff --git a/model/DataQuery.php b/model/DataQuery.php
index 2e5c66866..9b47a58e7 100644
--- a/model/DataQuery.php
+++ b/model/DataQuery.php
@@ -123,7 +123,8 @@ class DataQuery {
 
 		$this->query->setFrom("\"$baseClass\"");
 
-		singleton($this->dataClass)->extend('augmentDataQueryCreation', $this->query, $this);
+		$obj = Injector::inst()->get($baseClass);
+		$obj->extend('augmentDataQueryCreation', $this->query, $this);
 	}
 
 	function setQueriedColumns($queriedColumns) {
@@ -225,7 +226,9 @@ class DataQuery {
 		$query->selectField("CASE WHEN \"$baseClass\".\"ClassName\" IS NOT NULL THEN \"$baseClass\".\"ClassName\" ELSE '$baseClass' END", "RecordClassName");
 
 		// TODO: Versioned, Translatable, SiteTreeSubsites, etc, could probably be better implemented as subclasses of DataQuery
-		singleton($this->dataClass)->extend('augmentSQL', $query, $this);
+
+		$obj = Injector::inst()->get(ClassInfo::baseDataClass($this->dataClass));
+		$obj->extend('augmentSQL', $query, $this);
 
 		$this->ensureSelectContainsOrderbyColumns($query);
 
diff --git a/tests/core/ObjectTest.php b/tests/core/ObjectTest.php
index 6e62ad276..b64492bce 100644
--- a/tests/core/ObjectTest.php
+++ b/tests/core/ObjectTest.php
@@ -11,9 +11,7 @@ class ObjectTest extends SapphireTest {
 	
 	function setUp() {
 		parent::setUp();
-		
-		global $_SINGLETONS;
-		$_SINGLETONS = array();
+		Injector::inst()->unregisterAllObjects();
 	}
 	
 	function testHasmethodBehaviour() {