diff --git a/wp-includes/comment.php b/wp-includes/comment.php
index 53e2233dc3..b4f4125cc8 100644
--- a/wp-includes/comment.php
+++ b/wp-includes/comment.php
@@ -983,7 +983,7 @@ function wp_new_comment( $commentdata ) {
 	$commentdata['comment_parent'] = ( 'approved' == $parent_status || 'unapproved' == $parent_status ) ? $commentdata['comment_parent'] : 0;
 
 	$commentdata['comment_author_IP'] = preg_replace( '/[^0-9a-fA-F:., ]/', '',$_SERVER['REMOTE_ADDR'] );
-	$commentdata['comment_agent']     = $_SERVER['HTTP_USER_AGENT'];
+	$commentdata['comment_agent']     = substr($_SERVER['HTTP_USER_AGENT'], 0, 254);
 
 	$commentdata['comment_date']     = current_time('mysql');
 	$commentdata['comment_date_gmt'] = current_time('mysql', 1);