diff --git a/core/control/HTTPRequest.php b/core/control/HTTPRequest.php
index 6689a4ae9..6494739e8 100644
--- a/core/control/HTTPRequest.php
+++ b/core/control/HTTPRequest.php
@@ -330,7 +330,7 @@ class HTTPRequest extends Object implements ArrayAccess {
 				if($varRequired && !isset($this->dirParts[$i])) return false;
 				
 				$arguments[$varName] = isset($this->dirParts[$i]) ? $this->dirParts[$i] : null;
-				if($part == '$Controller' && !class_exists($arguments['Controller'])) {
+				if($part == '$Controller' && (!class_exists($arguments['Controller']) || !is_subclass_of($arguments['Controller'], 'RequestHandlingData'))) {
 					return false;
 				}
 				
diff --git a/core/model/DataObject.php b/core/model/DataObject.php
index d41a39f76..8abb3d4ff 100644
--- a/core/model/DataObject.php
+++ b/core/model/DataObject.php
@@ -2632,7 +2632,7 @@ class DataObject extends ViewableData implements DataObjectInterface {
 	 * which could cause horrible bugs.
 	 */
 	public static function set_context_obj($obj) {
-		if($obj && self::$context_obj) user_error("Dataobject::set_context_obj called when there is already a context.", E_USER_WARNING);
+		if($obj && self::$context_obj) user_error("Dataobject::set_context_obj passed " . $obj->class . "." . $obj->ID . " when there is already a context: " . self::$context_obj->class . '.' . self::$context_obj->ID, E_USER_WARNING);
 		self::$context_obj = $obj;
 	}
 
diff --git a/core/model/SiteTree.php b/core/model/SiteTree.php
index 867d7780a..ceeb0da56 100644
--- a/core/model/SiteTree.php
+++ b/core/model/SiteTree.php
@@ -865,7 +865,10 @@ class SiteTree extends DataObject {
 			'';
 
 		$count = 1;
-		while(class_exists($this->URLSegment) || DataObject::get_one("SiteTree", "URLSegment = '$this->URLSegment' $idFilter")) {
+		while (
+			(class_exists($this->URLSegment) && is_subclass_of($this->URLSegment, 'RequestHandlingData')) ||
+			DataObject::get_one("SiteTree", "URLSegment = '$this->URLSegment' $idFilter")
+		) {
 			$count++;
 			$this->URLSegment = ereg_replace('-[0-9]+$','', $this->URLSegment) . "-$count";
 		}
diff --git a/tests/SiteTreeTest.php b/tests/SiteTreeTest.php
index 14f4d8aca..ce9ae4364 100644
--- a/tests/SiteTreeTest.php
+++ b/tests/SiteTreeTest.php
@@ -12,6 +12,7 @@ class SiteTreeTest extends SapphireTest {
 	 *  - Turns things into lowercase-hyphen-format
 	 *  - Generates from Title by default, unless URLSegment is explicitly set
 	 *  - Resolves duplicates by appending a number
+	 *  - renames classes with a class name conflict
 	 */
 	function testURLGeneration() {
 		$expectedURLs = array(
@@ -23,6 +24,8 @@ class SiteTreeTest extends SapphireTest {
 			'product2' => 'another-product',
 			'product3' => 'another-product-2',
 			'product4' => 'another-product-3',
+			'object'   => 'object',
+			'controller' => 'controller-2'
 		);
 		
 		foreach($expectedURLs as $fixture => $urlSegment) {
diff --git a/tests/SiteTreeTest.yml b/tests/SiteTreeTest.yml
index 29f4caef2..b12141b39 100644
--- a/tests/SiteTreeTest.yml
+++ b/tests/SiteTreeTest.yml
@@ -23,6 +23,10 @@ Page:
         Title: Another Product
     contact:
         Title: Contact Us
+    object:
+        Title: Object
+    controller:
+        Title: Controller
         
 ErrorPage:
     404: