diff --git a/core/lib/Drupal/Core/Extension/UpdateModuleHandler.php b/core/lib/Drupal/Core/Extension/UpdateModuleHandler.php
index 4b2dce5..dd82606 100644
--- a/core/lib/Drupal/Core/Extension/UpdateModuleHandler.php
+++ b/core/lib/Drupal/Core/Extension/UpdateModuleHandler.php
@@ -17,17 +17,37 @@
  */
 class UpdateModuleHandler extends ModuleHandler {
 
+  /**
+   * Whether hook invocations are locked down to an explicit whitelist.
+   *
+   * @var bool
+   */
   protected $locked = FALSE;
 
+  /**
+   * Returns whether hook invocations are locked down to an explicit whitelist.
+   *
+   * @return bool
+   */
   public function isLocked() {
     return $this->locked;
   }
 
+  /**
+   * Locks down hook invocations to an explicit whitelist.
+   *
+   * Called right before update functions are executed.
+   */
   public function lock() {
     $this->locked = TRUE;
     return $this;
   }
 
+  /**
+   * Unlocks hook invocations.
+   *
+   * Called after update functions have been executed.
+   */
   public function unlock() {
     $this->locked = FALSE;
     return $this;
@@ -37,9 +57,11 @@ public function unlock() {
    * {@inheritdoc}
    */
   public function getImplementations($hook) {
-    if (!$this->isLocked) {
+    // If not running update functions, all hooks can be invoked.
+    if (!$this->isLocked()) {
       return parent::getImplementations($hook);
     }
+
     if (substr($hook, -6) === '_alter') {
       return array();
     }
diff --git a/core/update.php b/core/update.php
index 106a135..9600d3d 100644
--- a/core/update.php
+++ b/core/update.php
@@ -444,7 +444,9 @@ function update_task_list($active = NULL) {
     // Regular batch ops : defer to batch processing API.
     default:
       update_task_list('run');
+      \Drupal::moduleHandler()->lock();
       $output = _batch_page($request);
+      \Drupal::moduleHandler()->unlock();
       break;
   }
 }