diff --git a/Classes/Testing/BaseTestCase.php b/Classes/Testing/BaseTestCase.php
index b591d3ad..17c7a45e 100644
--- a/Classes/Testing/BaseTestCase.php
+++ b/Classes/Testing/BaseTestCase.php
@@ -462,7 +462,7 @@ protected function getAccessibleMock(
      */
     protected function buildAccessibleProxy($className)
     {
-        $accessibleClassName = uniqid($className);
+        $accessibleClassName = uniqid(str_replace('\\', '_', $className));
         $class = new ReflectionClass($className);
         $abstractModifier = $class->isAbstract() ? 'abstract ' : '';
 
diff --git a/composer.json b/composer.json
index ca391fbb..ffb59520 100644
--- a/composer.json
+++ b/composer.json
@@ -86,7 +86,7 @@
 		"bin-dir": ".Build/bin",
 		"sort-packages": true,
 		"preferred-install": {
-			"typo3/cms": "source"
+			"*": "dist"
 		},
 		"allow-plugins": {
 			"typo3/cms-composer-installers": true,