diff --git a/wp-includes/media.php b/wp-includes/media.php
index dc625d0116..61e31e808f 100644
--- a/wp-includes/media.php
+++ b/wp-includes/media.php
@@ -73,7 +73,7 @@ function image_downsize($id, $size = 'medium') {
 	}
 	elseif ( $size == 'thumbnail' ) {
 		// fall back to the old thumbnail
-		if ( $thumb_file = wp_get_attachment_thumb_file() && $info = getimagesize($thumb_file) ) {
+		if ( ($thumb_file = wp_get_attachment_thumb_file($id)) && $info = getimagesize($thumb_file) ) {
 			$img_url = str_replace(basename($img_url), basename($thumb_file), $img_url);
 			$width = $info[0];
 			$height = $info[1];