diff --git a/phpBB/includes/functions.php b/phpBB/includes/functions.php
index 3480a338c0..a0e2a46f54 100644
--- a/phpBB/includes/functions.php
+++ b/phpBB/includes/functions.php
@@ -2356,6 +2356,10 @@ function build_url($strip_vars = false)
 	{
 		$redirect = $phpbb_path_helper->strip_url_params($redirect, $strip_vars, false);
 	}
+	else
+	{
+		$redirect = str_replace('&', '&', $redirect);
+	}
 
 	return $redirect . ((strpos($redirect, '?') === false) ? '?' : '');
 }
diff --git a/tests/functions/build_url_test.php b/tests/functions/build_url_test.php
index 795427ffe8..ad36f29b8c 100644
--- a/tests/functions/build_url_test.php
+++ b/tests/functions/build_url_test.php
@@ -44,6 +44,11 @@ class phpbb_build_url_test extends phpbb_test_case
 				't',
 				'phpBB/index.php?',
 			),
+			array(
+				'viewtopic.php?t=5&f=4',
+				false,
+				'phpBB/viewtopic.php?t=5&f=4',
+			),
 			array(
 				'viewtopic.php?f=2&style=1&t=6',
 				'f',