diff --git a/src/wp-admin/includes/upgrade.php b/src/wp-admin/includes/upgrade.php
index 5692e36e81..6959a4d1b3 100644
--- a/src/wp-admin/includes/upgrade.php
+++ b/src/wp-admin/includes/upgrade.php
@@ -3339,6 +3339,7 @@ function make_site_theme_from_default( $theme_name, $template ) {
 			foreach ( $headers as $header => $value ) {
 				if ( strpos( $line, $header ) !== false ) {
 					$line = $header . ' ' . $value;
+					break;
 				}
 			}