diff -u b/core/lib/Drupal/Core/Config/FileStorage.php b/core/lib/Drupal/Core/Config/FileStorage.php
--- b/core/lib/Drupal/Core/Config/FileStorage.php
+++ b/core/lib/Drupal/Core/Config/FileStorage.php
@@ -298,18 +298,20 @@
     foreach (new \DirectoryIterator($directory) as $fileinfo) {
       if ($fileinfo->isDir() && !$fileinfo->isDot()) {
         $collection = $fileinfo->getFilename();
-        // Discover if there are sub directories representing a dotted
-        // collection name.
+        // Recursively call getAllCollectionNamesHelper() to discover if there
+        // are subdirectories. Subdirectories represent a dotted collection
+        // name.
         $sub_collections = $this->getAllCollectionNamesHelper($directory . '/' . $collection);
         if (!empty($sub_collections)) {
-          // Build up the collection name be concatenating the subdirectory
+          // Build up the collection name by concatenating the subdirectory
           // names with the current directory name.
           foreach ($sub_collections as $sub_collection) {
             $collections[] = $collection . '.' . $sub_collection;
           }
         }
         else {
-          //
+          // The directory has no subdirectories. Therefore add each directory
+          // to list of collections to be returned by the helper.
           $collections[] = $collection;
         }
       }