diff --git a/src/Configuration/Filesystem/FilesystemConfigurationSourceFactory.php b/src/Configuration/Filesystem/FilesystemConfigurationSourceFactory.php
index 1d1075b..0ec7aa8 100644
--- a/src/Configuration/Filesystem/FilesystemConfigurationSourceFactory.php
+++ b/src/Configuration/Filesystem/FilesystemConfigurationSourceFactory.php
@@ -45,6 +45,7 @@ public function buildConfiguration(ArrayNodeDefinition $node): void
             ->arrayNode('directories')
                 ->defaultValue(['%kernel.project_dir%/themes'])
                 ->requiresAtLeastOneElement()
+                ->performNoDeepMerging()
                 ->prototype('scalar')
         ;
     }