diff --git a/wp-includes/comment-template.php b/wp-includes/comment-template.php
index 3d32132146..c791ca6990 100644
--- a/wp-includes/comment-template.php
+++ b/wp-includes/comment-template.php
@@ -1643,13 +1643,13 @@ function comment_form( $args = array(), $post_id = null ) {
 	?>
 		<?php if ( comments_open( $post_id ) ) : ?>
 			<?php do_action( 'comment_form_before' ); ?>
-			<div id="respond">
-				<h3 id="reply-title"><?php comment_form_title( $args['title_reply'], $args['title_reply_to'] ); ?> <small><?php cancel_comment_reply_link( $args['cancel_reply_link'] ); ?></small></h3>
+			<div id="respond" class="comment-respond">
+				<h3 id="reply-title" class="comment-reply-title"><?php comment_form_title( $args['title_reply'], $args['title_reply_to'] ); ?> <small><?php cancel_comment_reply_link( $args['cancel_reply_link'] ); ?></small></h3>
 				<?php if ( get_option( 'comment_registration' ) && !is_user_logged_in() ) : ?>
 					<?php echo $args['must_log_in']; ?>
 					<?php do_action( 'comment_form_must_log_in_after' ); ?>
 				<?php else : ?>
-					<form action="<?php echo site_url( '/wp-comments-post.php' ); ?>" method="post" id="<?php echo esc_attr( $args['id_form'] ); ?>"<?php echo $html5 ? ' novalidate' : ''; ?>>
+					<form action="<?php echo site_url( '/wp-comments-post.php' ); ?>" method="post" id="<?php echo esc_attr( $args['id_form'] ); ?>" class="comment-form"<?php echo $html5 ? ' novalidate' : ''; ?>>
 						<?php do_action( 'comment_form_top' ); ?>
 						<?php if ( is_user_logged_in() ) : ?>
 							<?php echo apply_filters( 'comment_form_logged_in', $args['logged_in_as'], $commenter, $user_identity ); ?>