diff --git a/core/modules/simpletest/src/WebTestBase.php b/core/modules/simpletest/src/WebTestBase.php
index 240f9f2..833270d 100644
--- a/core/modules/simpletest/src/WebTestBase.php
+++ b/core/modules/simpletest/src/WebTestBase.php
@@ -1488,7 +1488,7 @@ protected function drupalGet($path, array $options = array(), array $headers = a
 
       $verbose = 'GET request to: ' . $path . '<hr />Ending URL: ' . $this->getUrl();
       if ($this->dumpHeaders) {
-        $verbose .= '<hr />Headers: <pre>' . check_plain(var_export(array_map('trim', $this->headers), TRUE)) . '</pre>';
+        $verbose .= '<hr />Headers: <pre>' . String::checkPlain(var_export(array_map('trim', $this->headers), TRUE)) . '</pre>';
       }
 	  $verbose .= '<hr />' . $out;