diff --git a/package_manager/src/PathExcluder/UnknownPathExcluder.php b/package_manager/src/PathExcluder/UnknownPathExcluder.php
index 7e39482a7b18881ae299f3be24fbbb69995ca113..91e4719701539bdbae96a4c14cbd67488bdea87f 100644
--- a/package_manager/src/PathExcluder/UnknownPathExcluder.php
+++ b/package_manager/src/PathExcluder/UnknownPathExcluder.php
@@ -66,14 +66,12 @@ final class UnknownPathExcluder implements EventSubscriberInterface {
    *   See \Drupal\package_manager\ComposerInspector::validate().
    */
   public function excludeUnknownPaths(CollectPathsToExcludeEvent $event): void {
-    $known_paths = [];
-
     $web_root = $this->pathLocator->getWebRoot();
     // If the web root and project root are the same, there's nothing to do.
     if (empty($web_root)) {
       return;
     }
-    $known_paths[] = $web_root;
+    $known_paths[] = [$web_root];
 
     $project_root = $this->pathLocator->getProjectRoot();
     // To determine the scaffold files to exclude, the installed packages must