diff --git a/core/lib/Drupal/Core/ExtensionHandler.php b/core/lib/Drupal/Core/ExtensionHandler.php
index 66c2150..9170824 100644
--- a/core/lib/Drupal/Core/ExtensionHandler.php
+++ b/core/lib/Drupal/Core/ExtensionHandler.php
@@ -373,9 +373,9 @@ public function alter($type, &$data, &$context1 = NULL, &$context2 = NULL) {
       $cid = $type;
     }
 
-    // Some alter hooks are invoked many times per page request, so statically
-    // cache the list of functions to call, and on subsequent calls, iterate
-    // through them quickly.
+    // Some alter hooks are invoked many times per page request, so store the
+    // list of functions to call, and on subsequent calls, iterate through them
+    // quickly.
     if (!isset($this->alterFunctions[$cid])) {
       $this->alterFunctions[$cid] = array();
       $hook = $type . '_alter';
@@ -404,7 +404,7 @@ public function alter($type, &$data, &$context1 = NULL, &$context2 = NULL) {
         // $this->alter('module_implements').
         if (array_diff($extra_modules, $modules)) {
           // Merge the arrays and order by getEnabledModules().
-          $modules = array_intersect($this->moduleList, array_merge($modules, $extra_modules));
+          $modules = array_intersect(array_keys($this->moduleList), array_merge($modules, $extra_modules));
           // Since $this->moduleImplements() already took care of loading the necessary
           // include files, we can safely pass FALSE for the array values.
           $implementations = array_fill_keys($modules, FALSE);