diff --git a/core/modules/simpletest/src/TestBase.php b/core/modules/simpletest/src/TestBase.php
index 028a086..82ee621 100644
--- a/core/modules/simpletest/src/TestBase.php
+++ b/core/modules/simpletest/src/TestBase.php
@@ -659,9 +659,11 @@ protected function assertNotNull($value, $message = '', $group = 'Other') {
    *   TRUE if the assertion succeeded, FALSE otherwise.
    */
   protected function assertEqual($first, $second, $message = '', $group = 'Other') {
-    // We cast objects implementing SafeStringInterface to string ourself so as
-    // to not rely on PHP casting them to string depending on what we're
+    // Cast objects implementing SafeStringInterface to string instead of
+    // relying on PHP casting them to string depending on what they are being
     // comparing with.
+    $first = $this->castSafeStrings($first);
+    $second = $this->castSafeStrings($second);
     return $this->assert($this->castSafeStrings($first) == $this->castSafeStrings($second), $message ? $message : SafeMarkup::format('Value @first is equal to value @second.', array('@first' => var_export($first, TRUE), '@second' => var_export($second, TRUE))), $group);
   }