diff --git a/core/lib/Drupal/Core/Template/TwigPhpStorageCache.php b/core/lib/Drupal/Core/Template/TwigPhpStorageCache.php
index bcc6786..4f1a2ce 100644
--- a/core/lib/Drupal/Core/Template/TwigPhpStorageCache.php
+++ b/core/lib/Drupal/Core/Template/TwigPhpStorageCache.php
@@ -83,7 +83,7 @@ public function generateKey($name, $className) {
       $name = basename($name);
     }
 
-    // If the suffix is longer that 61 characters then we truncate it so the
+    // If the suffix is longer that 51 characters then we truncate it so the
     // length of the filename can't grow beyond that. Windows only supports 255
     // characters in a path. If the files directory is in the usual place of
     // 'sites/default/files' then the maximum relative path of a twig file is
diff --git a/core/modules/system/system.post_update.php b/core/modules/system/system.post_update.php
index 59a49a4..d849106 100644
--- a/core/modules/system/system.post_update.php
+++ b/core/modules/system/system.post_update.php
@@ -57,3 +57,11 @@ function system_post_update_add_region_to_entity_displays() {
   array_map($entity_save, EntityViewDisplay::loadMultiple());
   array_map($entity_save, EntityFormDisplay::loadMultiple());
 }
+
+
+/**
+ * Force Twig php file cache to be cleared.
+ */
+function system_post_update_clear_twig_cache() {
+  // Empty post-update hook.
+}