Index: wp-includes/formatting.php
===================================================================
--- wp-includes/formatting.php	(revision 14218)
+++ wp-includes/formatting.php	(working copy)
@@ -2435,8 +2435,20 @@
 			break;
 
 		case 'siteurl':
+			$value = esc_url_raw($value);
+			if ( $value == '' && function_exists('add_settings_error') )
+			{
+				$value = get_option( $option ); // Resets option to stored val in case of empty
+				add_settings_error('siteurl', 'invalid_siteurl', __('The WordPress address you submitted was not in the right format. Please enter a valid URL.'));
+			}
+			break;
 		case 'home':
 			$value = esc_url_raw($value);
+			if ( $value == '' && function_exists('add_settings_error') )
+			{
+				$value = get_option( $option ); // Resets option to stored val in case of empty
+				add_settings_error('home', 'invalid_home', __('The Site address you submitted was not in the right format. Please enter a valid URL.'));
+			}
 			break;
 		default :
 			$value = apply_filters("sanitize_option_{$option}", $value, $option);