diff --git a/core/lib/Drupal/Core/Extension/ModuleHandler.php b/core/lib/Drupal/Core/Extension/ModuleHandler.php
index 364e0aa..d0ef571 100644
--- a/core/lib/Drupal/Core/Extension/ModuleHandler.php
+++ b/core/lib/Drupal/Core/Extension/ModuleHandler.php
@@ -10,6 +10,7 @@
 use Drupal\Component\Graph\Graph;
 use Drupal\Component\Serialization\Yaml;
 use Drupal\Component\Utility\NestedArray;
+use Drupal\Component\Utility\String;
 use Drupal\Core\Cache\CacheBackendInterface;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 
@@ -579,15 +580,10 @@ protected function buildImplementationInfo($hook) {
         if ($group) {
           $this->loadInclude($module, 'inc', "$module.$group");
         }
-        // It is possible that a module removed a hook implementation without
-        // the implementations cache being rebuilt yet, so we check whether the
-        // function exists on each request to avoid undefined function errors.
-        // Since ModuleHandler::implementsHook() may needlessly try to
-        // load the include file again, function_exists() is used directly here.
+        // If a new implementation was added, verify that the function exists.
         if (!function_exists($module . '_' . $hook)) {
-          // Clear out the stale implementation from the cache and force a cache
-          // refresh to forget about no longer existing hook implementations.
-          unset($implementations[$module]);
+          $function = String::checkPlain($module . '_' . $hook);
+          throw new \Exception("An invalid implementation '$function' was added by hook_module_implements_alter()");
         }
       }
     }