diff -u b/core/modules/field_ui/src/DisplayOverviewBase.php b/core/modules/field_ui/src/DisplayOverviewBase.php
--- b/core/modules/field_ui/src/DisplayOverviewBase.php
+++ b/core/modules/field_ui/src/DisplayOverviewBase.php
@@ -406,7 +406,7 @@
         if (!empty($summary)) {
           $field_row['settings_summary'] = array(
             '#type' => 'twig_inline',
-            '#template' => '<div class="field-plugin-summary">{{ summary|join("<br />") }}</div>',
+            '#template' => '<div class="field-plugin-summary">{{ summary|safe_join("<br />") }}</div>',
             '#context' => array('summary' => $summary),
             '#cell_attributes' => array('class' => array('field-plugin-summary-cell')),
           );