diff --git a/wp-includes/comment-template.php b/wp-includes/comment-template.php
index 77f16d9ab2..2f1c59ee5d 100644
--- a/wp-includes/comment-template.php
+++ b/wp-includes/comment-template.php
@@ -2252,6 +2252,9 @@ function comment_form( $args = array(), $post_id = null ) {
 	 */
 	$args = wp_parse_args( $args, apply_filters( 'comment_form_defaults', $defaults ) );
 
+	// Ensure that the filtered args contain all required default values.
+	$args = array_merge( $defaults, $args );
+
 		if ( comments_open( $post_id ) ) : ?>
 			<?php
 			/**
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 9434da0289..e26adb366e 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.3-alpha-32510';
+$wp_version = '4.3-alpha-32511';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.