diff --git a/core/lib/Drupal/Component/Utility/SafeMarkup.php b/core/lib/Drupal/Component/Utility/SafeMarkup.php
index 56bd518..5bf096f 100644
--- a/core/lib/Drupal/Component/Utility/SafeMarkup.php
+++ b/core/lib/Drupal/Component/Utility/SafeMarkup.php
@@ -153,6 +153,23 @@ public static function checkAdminXss($string) {
   }
 
   /**
+   * Filters field separators.
+   *
+   * Strings smaller than 3 characters will not be set as safe. This should
+   * never be a problem because even the smallest HTML tags, such as "<p>",
+   * require 3.
+   *
+   * @param string $string
+   *   A string.
+   *
+   * @return string
+   *   The filtered string, which is marked as safe if longer than 2 characters.
+   */
+  public static function filterSeparator($string) {;
+    return Unicode::strlen($string) < 3 ? $string : Xss::filterAdmin($string);
+  }
+
+  /**
   * Retrieves all strings currently marked as safe.
   *
   * This is useful for the batch and form APIs, where it is important to
diff --git a/core/modules/field/src/Plugin/views/field/Field.php b/core/modules/field/src/Plugin/views/field/Field.php
index 7fdc28b..908bcb0 100644
--- a/core/modules/field/src/Plugin/views/field/Field.php
+++ b/core/modules/field/src/Plugin/views/field/Field.php
@@ -701,7 +701,7 @@ protected function renderItems($items) {
       if ($this->options['multi_type'] == 'separator') {
         $output = '';
         $separator = '';
-        $escaped_separator = Xss::filterAdmin($this->options['separator']);
+        $escaped_separator = SafeMarkup::filterSeparator($this->options['separator']);
         foreach ($items as $item) {
           $output .= $separator . SafeMarkup::escape($item);
           $separator = $escaped_separator;
diff --git a/core/modules/views/views.theme.inc b/core/modules/views/views.theme.inc
index 4e007ad..700b389 100644
--- a/core/modules/views/views.theme.inc
+++ b/core/modules/views/views.theme.inc
@@ -132,7 +132,7 @@ function template_preprocess_views_view_fields(&$variables) {
       }
 
       if (!empty($variables['options']['separator']) && $previous_inline && $object->inline && $object->content) {
-        $object->separator = Xss::filterAdmin($variables['options']['separator']);
+        $object->separator = SafeMarkup::filterSeparator($variables['options']['separator']);
       }
 
       $object->class = Html::cleanCssIdentifier($id);
@@ -388,7 +388,7 @@ function template_preprocess_views_view_summary_unformatted(&$variables) {
   foreach ($variables['rows'] as $id => $row) {
     // Only false on first time.
     if ($count++) {
-      $variables['rows'][$id]->separator = Xss::filterAdmin($variables['options']['separator']);
+      $variables['rows'][$id]->separator = SafeMarkup::filterSeparator($variables['options']['separator']);
     }
     $variables['rows'][$id]->attributes = array();
     $variables['rows'][$id]->link = $argument->summaryName($row);
@@ -578,7 +578,7 @@ function template_preprocess_views_view_table(&$variables) {
           if (!empty($column_reference['content'])) {
             if (!empty($options['info'][$column]['separator'])) {
               $safe_content = SafeMarkup::escape($column_reference['content']);
-              $safe_separator = Xss::filterAdmin($options['info'][$column]['separator']);
+              $safe_separator = SafeMarkup::filterSeparator($options['info'][$column]['separator']);
               $column_reference['content'] = SafeMarkup::set($safe_content . $safe_separator);
             }
           }
diff --git a/core/tests/Drupal/Tests/Component/Utility/SafeMarkupTest.php b/core/tests/Drupal/Tests/Component/Utility/SafeMarkupTest.php
index eadc122..55fee39 100644
--- a/core/tests/Drupal/Tests/Component/Utility/SafeMarkupTest.php
+++ b/core/tests/Drupal/Tests/Component/Utility/SafeMarkupTest.php
@@ -101,4 +101,23 @@ public function testInvalidSetMultiple() {
     SafeMarkup::setMultiple($texts);
   }
 
+  /**
+   * Tests SafeMarkup::filterSeparator().
+   *
+   * @covers ::filterSeparator
+   */
+  public function testFilterSeparator() {
+    $returned = SafeMarkup::filterSeparator('<br />');
+    $this->assertEquals('<br />', $returned, 'Separator string "<br />" was not modified.');
+    $this->assertTrue(SafeMarkup::isSafe($returned), 'Separator string "<br />" was marked as safe');
+    $returned = SafeMarkup::filterSeparator('---');
+    $this->assertEquals('---', $returned, 'Separator string "---" was not modified');
+    $this->assertTrue(SafeMarkup::isSafe($returned), 'Separator string "---" was marked as safe');
+    $returned = SafeMarkup::filterSeparator('<');
+    $this->assertEquals('<', $returned, 'Separator string "<" was not modified');
+    $this->assertFalse(SafeMarkup::isSafe($returned), 'Separator string "<" was not marked as safe');
+    $returned = SafeMarkup::filterSeparator('<script>alert("hello");</script>');
+    $this->assertEquals('alert("hello");', $returned, 'Separator string "<script>alert("hello");</script>" was modified');
+    $this->assertTrue(SafeMarkup::isSafe($returned), 'Modified separator string "alert("hello");" was marked as safe');
+  }
 }
diff --git a/core/themes/engines/twig/twig.engine b/core/themes/engines/twig/twig.engine
index 5ef2f10..84cd53a 100644
--- a/core/themes/engines/twig/twig.engine
+++ b/core/themes/engines/twig/twig.engine
@@ -279,7 +279,7 @@ function twig_drupal_join_filter($value, $glue = '') {
   $output = '';
   foreach ($value as $item) {
     $output .= $separator . SafeMarkup::escape($item);
-    $separator = $glue;
+    $separator = SafeMarkup::filterSeparator($glue);
   }
 
   return SafeMarkup::set($output);