diff --git a/package_manager/src/PathExcluder/SiteConfigurationExcluder.php b/package_manager/src/PathExcluder/SiteConfigurationExcluder.php
index 96c29f006061b46dff81c7f22f4101f9d3b936de..0c4bd7b498ccf2c91c47af924bcbdc569bc3d832 100644
--- a/package_manager/src/PathExcluder/SiteConfigurationExcluder.php
+++ b/package_manager/src/PathExcluder/SiteConfigurationExcluder.php
@@ -86,25 +86,41 @@ class SiteConfigurationExcluder implements EventSubscriberInterface {
    *   The event being handled.
    *
    * @throws \Drupal\Core\File\Exception\FileException
-   *   If the permissions of the live `sites/default` cannot be determined, or
-   *   changed on the staged `sites/default`.
+   *   If the permissions of the either the live or staged `sites/default`
+   *   cannot be determined, or changed on the staged `sites/default`.
    */
   public function syncDefaultSiteDirectoryPermissions(PreApplyEvent $event): void {
     $live_dir = $this->getDefaultSiteDirectoryPath($this->pathLocator->getProjectRoot());
     $staged_dir = $this->getDefaultSiteDirectoryPath($event->stage->getStageDirectory());
 
-    $original_permissions = fileperms($live_dir);
-    if ($original_permissions === FALSE) {
-      throw new FileException("Could not determine permissions for '$live_dir'.");
-    }
+    // This is borrowed from \Symfony\Component\Filesystem\Filesystem::copy().
+    $permissions = $this->getPermissions($staged_dir) | ($this->getPermissions($live_dir) & 0111);
 
-    // @see \Symfony\Component\Filesystem\Filesystem::copy() for another use
-    // of the 0111 bitmask.
-    if (!$this->fileSystem->chmod($staged_dir, $original_permissions & 0111)) {
+    if (!$this->fileSystem->chmod($staged_dir, $permissions)) {
       throw new FileException("Could not change permissions on '$staged_dir'.");
     }
   }
 
+  /**
+   * Gets the current file permissions of a path.
+   *
+   * @param string $path
+   *   The path to examine.
+   *
+   * @return int
+   *   The current permissions of the path.
+   *
+   * @throws \Drupal\Core\File\Exception\FileException
+   *   Thrown if the file permissions cannot be determined.
+   */
+  private function getPermissions(string $path): int {
+    $permissions = fileperms($path);
+    if ($permissions === FALSE) {
+      throw new FileException("Could not determine permissions for '$path'.");
+    }
+    return $permissions;
+  }
+
   /**
    * Returns the full path to `sites/default`, relative to a root directory.
    *