diff --git a/core/modules/file/src/Tests/DownloadTest.php b/core/modules/file/src/Tests/DownloadTest.php
index 54f3da7..83064a6 100644
--- a/core/modules/file/src/Tests/DownloadTest.php
+++ b/core/modules/file/src/Tests/DownloadTest.php
@@ -86,9 +86,9 @@ protected function doPrivateFileTransferTest() {
     $this->assertEqual($contents, $this->content, 'Contents of the file are correct.');
 
     // Deny access to all downloads via a -1 header.
-    file_test_set_return('download', -1);
+    file_test_set_return('download', NULL);
     $this->drupalHead($url);
-    $this->assertResponse(403, 'Correctly denied access to a file when file_test sets the header to -1.');
+    $this->assertResponse(403, 'Correctly denied access to a file when no headers are sent.');
 
     // Try non-existent file.
     $url = file_create_url('private://' . $this->randomName());