diff --git a/tests/test_framework/phpbb_functional_test_case.php b/tests/test_framework/phpbb_functional_test_case.php
index 1725a45e38..4ebe1d2d17 100644
--- a/tests/test_framework/phpbb_functional_test_case.php
+++ b/tests/test_framework/phpbb_functional_test_case.php
@@ -468,6 +468,6 @@ class phpbb_functional_test_case extends phpbb_test_case
 		$content = self::$client->getResponse()->getContent();
 
 		// Any output before the doc type means there was an error
-		self::assertStringStartsWith('<!DOCTYPE', $content, 'Output found before DOCTYPE specification.');
+		self::assertStringStartsWith('<!DOCTYPE', trim($content), 'Output found before DOCTYPE specification.');
 	}
 }