diff -u b/core/tests/Drupal/FunctionalTests/AssertLegacyTrait.php b/core/tests/Drupal/FunctionalTests/AssertLegacyTrait.php
--- b/core/tests/Drupal/FunctionalTests/AssertLegacyTrait.php
+++ b/core/tests/Drupal/FunctionalTests/AssertLegacyTrait.php
@@ -2,7 +2,6 @@
 
 namespace Drupal\FunctionalTests;
 
-use Behat\Mink\Exception\ElementNotFoundException;
 use Behat\Mink\Exception\ExpectationException;
 use Behat\Mink\Selector\Xpath\Escaper;
 use Drupal\Component\Render\FormattableMarkup;
@@ -248,7 +247,7 @@
   }
 
   /**
-   * Asserts that a field exists with the given ID and val.ue.
+   * Asserts that a field exists with the given ID and value.
    *
    * @param string $id
    *   ID of field to assert.
@@ -613,8 +612,9 @@
       if ($fields) {
         foreach ($fields as $field) {
           if ($field->getAttribute('type') == 'checkbox') {
-            // Checkbox with the correct checked state.
-            $found = $field->isChecked() === $value;
+            // Checkbox with the correct checked state if the value was passed
+            // as a boolean.
+            $found = !is_bool($value) || $field->isChecked() === $value;
           }
           elseif ($field->getTagName() == 'select' && $field->find('xpath', '//option[@value = ' . (new Escaper())->escapeLiteral($value) . ' and @selected = "selected"]')) {
             // Select element with an option.