Index: wp-content/themes/twentythirteen/style.css
===================================================================
--- wp-content/themes/twentythirteen/style.css	(revision 23455)
+++ wp-content/themes/twentythirteen/style.css	(working copy)
@@ -2170,6 +2170,11 @@
 	padding-right: 376px;
 }
 
+.comment-list #respond #commentform {
+	max-width: 604px;
+	padding: 0;
+}
+
 .comments-title {
 	font: 300 italic 28px "Source Sans Pro", Helvetica, sans-serif;
 	padding: 30px 0 20px;