diff --git a/core/modules/help_topics/help_topics.module b/core/modules/help_topics/help_topics.module
index e9c6c4674c..2af0cb2996 100644
--- a/core/modules/help_topics/help_topics.module
+++ b/core/modules/help_topics/help_topics.module
@@ -64,10 +64,57 @@ function help_topics_rebuild() {
   // when a module or theme is installed, uninstalled, or updated; and when
   // languages are added, translations are changed, or string overrides are
   // changed. These situations can cause an indexed help item to have different
-  // text, or for help items to be added or removed. So, we use a state
-  // variable to keep track of the need to reindex.
+  // text, or for help items to be added or removed. We cannot detect all of
+  // these cases, so instead at least trigger a reindex on cache rebuild.
+  help_topics_update_help_search_index('reindex');
+}
+
+/**
+ * Implements hook_modules_uninstalled().
+ */
+function help_topics_modules_uninstalled(array $modules) {
+  help_topics_update_help_search_index('list');
+}
+
+/**
+ * Implements hook_themes_uninstalled().
+ */
+function help_topics_themes_uninstalled(array $themes) {
+  help_topics_update_help_search_index('list');
+}
+
+/**
+ * Updates the full search index or the topic list for help search.
+ *
+ * If there is currently an active help search page on the site, either the help
+ * topics that have been indexed for searching are marked for reindexing, or
+ * the list of topics is updated.
+ *
+ * @param string $action
+ *   'reindex' to mark all topics for reindexing, or 'list' (default) to only
+ *   update the topic list.
+ */
+function help_topics_update_help_search_index($action = 'list') {
+  if (!\Drupal::moduleHandler()->moduleExists('search')) {
+    return;
+  }
+
+  $search_page_repository = \Drupal::service('search.search_page_repository');
+  /** @var \Drupal\help_topics\Plugin\Search\HelpSearch $plugin */
+  $plugin = NULL;
+  foreach ($search_page_repository->getIndexableSearchPages() as $entity) {
+    if ($entity->get('plugin') == 'help_search') {
+      $plugin = $entity->getPlugin();
+      break;
+    }
+  }
 
-  if (\Drupal::moduleHandler()->moduleExists('search')) {
-    \Drupal::state()->set('help_search_reindex_needed', TRUE);
+  if ($plugin) {
+    if ($action === 'list') {
+      $plugin->updateTopicList();
+    }
+    elseif ($action === 'reindex') {
+      $plugin->markForReindex();
+    }
   }
 }
diff --git a/core/modules/help_topics/help_topics/help_topics.help_topic_search.html.twig b/core/modules/help_topics/help_topics/help_topics.help_topic_search.html.twig
index 394a74f75f..e18b5ad1d3 100644
--- a/core/modules/help_topics/help_topics/help_topics.help_topic_search.html.twig
+++ b/core/modules/help_topics/help_topics/help_topics.help_topic_search.html.twig
@@ -8,6 +8,7 @@
   <li>{% trans %}In the <em>Manage</em> administrative menu, navigate to <em>Configuration</em> &gt; <em>Search and metadata</em> &gt; <em>Search pages</em> (<em>admin/config/search/pages</em>).{% endtrans %}</li>
   <li>{% trans %}Verify that a Help search page is listed in the <em>Search pages</em> section. If not, add a new page of type <em>Help</em>.{% endtrans %}</li>
   <li>{% trans %}Check the indexing status of the Help search page. If it is not fully indexed, run Cron until indexing is complete.{% endtrans %}</li>
+  <li>{% trans %}In the future, you can click <em>Rebuild search index</em> on this page, or clear the site cache, in order to force help topic text to be reindexed for searching. This should be done whenever a module, theme, language, or string translation is updated.{% endtrans %}</li>
   <li>{% trans %}In the  <em>Manage</em> administrative menu, navigate to <em>Structure</em> &gt; <em>Block layout</em> (<em>admin/structure/block</em>).{% endtrans %}</li>
   <li>{% trans %}Click the link for your administrative theme (such as the core Seven theme), near the top of the page.{% endtrans %}</li>
   <li>{% trans %}See if there is already a help search block placed in the Help region of your administrative theme.{% endtrans %}</li>
diff --git a/core/modules/help_topics/src/Plugin/HelpSection/HelpTopicSection.php b/core/modules/help_topics/src/Plugin/HelpSection/HelpTopicSection.php
index c604d650ae..8af8688b38 100644
--- a/core/modules/help_topics/src/Plugin/HelpSection/HelpTopicSection.php
+++ b/core/modules/help_topics/src/Plugin/HelpSection/HelpTopicSection.php
@@ -150,6 +150,14 @@ public function getCacheMaxAge() {
     return $this->getCacheMetadata()->getCacheMaxAge();
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public function clearCachedDefinitions() {
+    parent::clearCachedDefinitions();
+    help_topics_update_help_search_index('reindex');
+  }
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/help_topics/src/Plugin/Search/HelpSearch.php b/core/modules/help_topics/src/Plugin/Search/HelpSearch.php
index 29c4f726ce..fc5daa2e88 100644
--- a/core/modules/help_topics/src/Plugin/Search/HelpSearch.php
+++ b/core/modules/help_topics/src/Plugin/Search/HelpSearch.php
@@ -292,10 +292,8 @@ protected function prepareResults(StatementInterface $found) {
    * {@inheritdoc}
    */
   public function updateIndex() {
-    // See if we need to update the list of items to be indexed.
-    if ($this->state->get('help_search_reindex_needed', TRUE)) {
-      $this->markForReindex();
-    }
+    // Update the list of items to be indexed.
+    $this->updateTopicList();
 
     // Find some items that need to be updated. Start with ones that have
     // never been indexed.
@@ -361,11 +359,11 @@ public function indexClear() {
   }
 
   /**
-   * {@inheritdoc}
+   * Rebuilds the database table containing topics to be indexed.
    */
-  public function markForReindex() {
-    // Update the list of help items. Start by fetching the existing list,
-    // so we can remove items not found at the end.
+  public function updateTopicList() {
+    // Start by fetching the existing list, so we can remove items not found
+    // at the end.
     $old_list = $this->database->select('help_search_items', 'hsi')
       ->fields('hsi', ['sid', 'topic_id', 'section_plugin_id', 'permission'])
       ->execute();
@@ -414,21 +412,21 @@ public function markForReindex() {
 
     // Remove remaining items from the index.
     $this->removeItemsFromIndex($sids_to_remove);
+  }
 
-    // Mark all items currently in the search index database as needing
-    // reindex.
+  /**
+   * {@inheritdoc}
+   */
+  public function markForReindex() {
+    $this->updateTopicList();
     search_mark_for_reindex($this->getType());
-    $this->state->set('help_search_reindex_needed', FALSE);
   }
 
   /**
    * {@inheritdoc}
    */
   public function indexStatus() {
-    if ($this->state->get('help_search_reindex_needed', TRUE)) {
-      $this->markForReindex();
-    }
-
+    $this->updateTopicList();
     $total = $this->database->select('help_search_items', 'hsi')
       ->countQuery()
       ->execute()
diff --git a/core/modules/help_topics/src/SearchableHelpInterface.php b/core/modules/help_topics/src/SearchableHelpInterface.php
index 06fdb939c1..701c7fd102 100644
--- a/core/modules/help_topics/src/SearchableHelpInterface.php
+++ b/core/modules/help_topics/src/SearchableHelpInterface.php
@@ -7,6 +7,10 @@
 /**
  * Provides an interface for a HelpSection plugin that also supports search.
  *
+ * Note that in addition to these methods, plugins that support search should
+ * also call help_topics_update_help_search_index('reindex') in their
+ * clearCachedDefinitions() method.
+ *
  * @see \Drupal\help\HelpSectionPluginInterface
  *
  * @internal
diff --git a/core/modules/help_topics/tests/src/Functional/HelpTopicSearchTest.php b/core/modules/help_topics/tests/src/Functional/HelpTopicSearchTest.php
index 5102ca3e17..1aeafad973 100644
--- a/core/modules/help_topics/tests/src/Functional/HelpTopicSearchTest.php
+++ b/core/modules/help_topics/tests/src/Functional/HelpTopicSearchTest.php
@@ -53,6 +53,10 @@ protected function setUp() {
     // here.
     $this->rebuildContainer();
 
+    // Before running cron, verify that a search returns no results.
+    $this->drupalPostForm('search/help', ['keys' => 'notawordenglish'], 'Search');
+    $this->assertSearchResultsCount(0);
+
     // Run cron until the topics are fully indexed, with a limit of 100 runs
     // to avoid infinite loops.
     $num_runs = 100;
@@ -191,6 +195,12 @@ public function testHelpSearch() {
     $this->drupalPostForm('search/help', ['keys' => 'notawordenglish'], 'Search');
     $this->assertSearchResultsCount(0);
     $session->pageTextContains('no results');
+
+    // Uninstall the test module and verify its topics are immediately not
+    // searchable.
+    \Drupal::service('module_installer')->uninstall(['help_topics_test']);
+    $this->drupalPostForm('search/help', ['keys' => 'nonworditem'], 'Search');
+    $this->assertSearchResultsCount(0);
   }
 
   /**