diff -u b/core/modules/system/theme.api.php b/core/modules/system/theme.api.php
--- b/core/modules/system/theme.api.php
+++ b/core/modules/system/theme.api.php
@@ -743,7 +743,7 @@
       'core/backbone',
     ],
   ];
-  if (Drupal::moduleHandler()->moduleExists('minizombies')) {
+  if (Drupal::moduleHandler()->moduleExists('minifyzombies')) {
     $libraries['mymodule.zombie'] += [
       'js' => [
         'mymodule.zombie.min.js' => [],
@@ -769,7 +769,7 @@
   // without reproducing this check. If the library definition does not exist
   // the library (of course) not be loaded but no notices or errors will be
   // triggered.
-  if (module_exists('vampireize')) {
+  if (Drupal::moduleHandler()->moduleExists('vampirize')) {
     $libraries['mymodule.vampire'] = [
       'js' => [
         'js/vampire.js' => [],