diff -u b/core/includes/bootstrap.inc b/core/includes/bootstrap.inc
--- b/core/includes/bootstrap.inc
+++ b/core/includes/bootstrap.inc
@@ -217,8 +217,8 @@
   // drupal_static().
   static $files = array();
 
-  // We use drupal static for the missing records so we can test it.
-  // Drupal static fast pattern is used as this function may be called often.
+  // We use drupal_static() for the missing records so we can test it.
+  // drupal_static_fast() is used as this function may be called often.
   static $drupal_static_fast;
   if (!isset($drupal_static_fast)) {
     $drupal_static_fast['missing'] = &drupal_static(__FUNCTION__ . ':missing');
diff -u b/core/modules/system/src/Tests/Bootstrap/GetFilenameUnitTest.php b/core/modules/system/src/Tests/Bootstrap/GetFilenameUnitTest.php
--- b/core/modules/system/src/Tests/Bootstrap/GetFilenameUnitTest.php
+++ b/core/modules/system/src/Tests/Bootstrap/GetFilenameUnitTest.php
@@ -90,6 +90,7 @@
     $missing = &drupal_static('drupal_get_filename:missing');
 
-    // Searching for an item that does not exist creates a static record in drupal_get_filename.
-    $this->assertTrue($missing['module'][$non_existing_module], 'Searching for an item that does not exist creates a static record in drupal_get_filename.');
+    // Searching for an item that does not exist creates a static record in
+    // drupal_get_filename().
+    $this->assertTrue($missing['module'][$non_existing_module], 'Searching for an item that does not exist creates a static record in drupal_get_filename().');
   }
 }