core/modules/search/src/Controller/SearchController.php   |  9 ++++++++-
 core/modules/search/src/Tests/SearchPageCacheTagsTest.php |  4 ++--
 core/modules/simpletest/src/WebTestBase.php               | 11 +++++++++++
 3 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/core/modules/search/src/Controller/SearchController.php b/core/modules/search/src/Controller/SearchController.php
index d49173a..3a14a7b 100644
--- a/core/modules/search/src/Controller/SearchController.php
+++ b/core/modules/search/src/Controller/SearchController.php
@@ -124,10 +124,17 @@ public function view(Request $request, SearchPageInterface $entity) {
         ),
       ),
       '#cache' => array(
-        'tags' => Cache::mergeTags($entity->getCacheTags(), ['search_index:' . $plugin->getPluginId()]),
+        'tags' => $entity->getCacheTags(),
       ),
     );
 
+    // If this plugin uses a search index, then also add the cache tag tracking
+    // that search index, so that cached search result pages are invalidated
+    // when necessary.
+    if ($plugin->getType() !== NULL) {
+      $build['search_results']['#cache']['tags'][] = 'search_index:' . $plugin->getType();
+    }
+
     $build['pager'] = array(
       '#type' => 'pager',
     );
diff --git a/core/modules/search/src/Tests/SearchPageCacheTagsTest.php b/core/modules/search/src/Tests/SearchPageCacheTagsTest.php
index eb33827..8f2e509 100644
--- a/core/modules/search/src/Tests/SearchPageCacheTagsTest.php
+++ b/core/modules/search/src/Tests/SearchPageCacheTagsTest.php
@@ -92,13 +92,13 @@ function testSearchText() {
     // Initial page for searching users.
     $this->drupalGet('search/user');
     $this->assertCacheTag('config:search.page.user_search');
-    $this->assertCacheTag('search_index:user_search');
+    $this->assertNoCacheTag('search_index:user_search');
 
     // User search results.
     $edit['keys'] = $this->searchingUser->getUsername();
     $this->drupalPostForm('search/user', $edit, t('Search'));
     $this->assertCacheTag('config:search.page.user_search');
-    $this->assertCacheTag('search_index:user_search');
+    $this->assertNoCacheTag('search_index:user_search');
   }
 
 }
diff --git a/core/modules/simpletest/src/WebTestBase.php b/core/modules/simpletest/src/WebTestBase.php
index e79dff9..3bb404d 100644
--- a/core/modules/simpletest/src/WebTestBase.php
+++ b/core/modules/simpletest/src/WebTestBase.php
@@ -2762,4 +2762,15 @@ protected function assertCacheTag($expected_cache_tag) {
     $this->assertTrue(in_array($expected_cache_tag, $cache_tags), "'" . $expected_cache_tag . "' is present in the X-Drupal-Cache-Tags header.");
   }
 
+  /**
+   * Asserts whether an expected cache tag was absent in the last response.
+   *
+   * @param string $expected_cache_tag
+   *   The expected cache tag.
+   */
+  protected function assertNoCacheTag($expected_cache_tag) {
+    $cache_tags = explode(' ', $this->drupalGetHeader('X-Drupal-Cache-Tags'));
+    $this->assertFalse(in_array($expected_cache_tag, $cache_tags), "'" . $expected_cache_tag . "' is absent in the X-Drupal-Cache-Tags header.");
+  }
+
 }