diff --git a/core/modules/file/src/Tests/FileManagedFileElementTest.php b/core/modules/file/src/Tests/FileManagedFileElementTest.php
index 61c00de..0de2ded 100644
--- a/core/modules/file/src/Tests/FileManagedFileElementTest.php
+++ b/core/modules/file/src/Tests/FileManagedFileElementTest.php
@@ -6,6 +6,7 @@
  */
 
 namespace Drupal\file\Tests;
+use Drupal\Component\Utility\Bytes;
 use Drupal\Component\Utility\SafeMarkup;
 use Drupal\file\Entity\File;
 
@@ -110,12 +111,11 @@ function testManagedFile() {
             $this->assertRaw(t('The file ids are %fids.', array('%fids' => '')), 'Submission after file upload and removal was successful.');
 
             // Upload a file which exceeds the configured post_max_size limit.
-            $post_max_size_init = ini_get('post_max_size');
-            if ($post_max_size_init) {
-              // Parse the upload size in order to produce a file bigger as it.
-              $regex = '/^([0-9]+)([bkmgtpezy])$/i';
-              preg_match($regex, $post_max_size_init, $match);
-              $post_max_size = round($match[1] * pow(1024, stripos('bkmgtpezy', strtolower($match[2]))));
+            $post_max_size_ini = ini_get('post_max_size');
+            if ($post_max_size_ini) {
+              $this->assertTrue(FALSE, ini_get('post_max_size'));
+              $this->assertTrue(FALSE, ini_get('upload_max_filesize'));
+              $post_max_size = Bytes::toInt($post_max_size_ini);
               $big_test_data = str_repeat('a', $post_max_size * 1.1);
               file_put_contents('public://test.dat', $big_test_data);