diff --git a/src/ParentPlugin.php b/src/ParentPlugin.php
index df0598a..c938ff5 100644
--- a/src/ParentPlugin.php
+++ b/src/ParentPlugin.php
@@ -12,7 +12,7 @@ use Composer\IO\IOInterface;
 use Composer\Plugin\PluginInterface;
 use TopFloor\ComposerCleanupVcsDirs\Plugin as TopFloorPlugin;
 
-if (class_exists(TopFloorPlugin::class,false)){
+if (file_exists(__DIR__.'/../../../topfloor/composer-cleanup-vcs-dirs/src/Plugin.php') && class_exists(TopFloorPlugin::class,true)){
     abstract class ParentPlugin extends TopFloorPlugin
     {
         /**