diff --git a/code/CMSMenu.php b/code/CMSMenu.php
index 5c97ac2e..4a5b5e1e 100644
--- a/code/CMSMenu.php
+++ b/code/CMSMenu.php
@@ -280,10 +280,15 @@ class CMSMenu extends Object implements IteratorAggregate, i18nEntityProvider
 		foreach($subClasses as $key => $className) {
 			// Remove abstract classes and LeftAndMain
 			$classReflection = new ReflectionClass($className);
-			if(!$classReflection->isInstantiable() || 'LeftAndMain' == $className) {
+			if(
+				!$classReflection->isInstantiable() 
+				|| 'LeftAndMain' == $className 
+				|| ClassInfo::classImplements($className, 'TestOnly')
+			) {
 				unset($subClasses[$key]);
 			}			
 		}
+		
 		return $subClasses;
 	}
 	
diff --git a/tests/ModelAdminTest.php b/tests/ModelAdminTest.php
index 91990bc3..d043800e 100644
--- a/tests/ModelAdminTest.php
+++ b/tests/ModelAdminTest.php
@@ -11,7 +11,7 @@ class ModelAdminTest extends FunctionalTest {
 	}
 }
 
-class ModelAdminTest_Admin extends ModelAdmin {
+class ModelAdminTest_Admin extends ModelAdmin implements TestOnly {
 	static $url_segment = 'testadmin';
 	
 	public static $managed_models = array(