Index: wp-includes/formatting.php
===================================================================
--- wp-includes/formatting.php	(revision 11733)
+++ wp-includes/formatting.php	(working copy)
@@ -2349,7 +2349,8 @@
 		case 'close_comments_days_old':
 		case 'comments_per_page':
 		case 'thread_comments_depth':
-			$value = abs((int) $value);
+		case 'users_can_register':
+			$value = absint( $value );
 			break;
 
 		case 'posts_per_page':