Index: wp-includes/query.php
===================================================================
--- wp-includes/query.php	(revision 13459)
+++ wp-includes/query.php	(working copy)
@@ -2021,16 +2021,18 @@
 			if ( !empty($q['meta_key']) ) {
 				$allowed_keys[] = $q['meta_key'];
 				$allowed_keys[] = 'meta_value';
+				$allowed_keys[] = 'meta_value_num';
 			}
 			$q['orderby'] = urldecode($q['orderby']);
 			$q['orderby'] = addslashes_gpc($q['orderby']);
-			$orderby_array = explode(' ',$q['orderby']);
-			if ( empty($orderby_array) )
-				$orderby_array[] = $q['orderby'];
+			$orderby_array = explode(' ', $q['orderby']);
 			$q['orderby'] = '';
-			for ($i = 0; $i < count($orderby_array); $i++) {
+
+			foreach ( $orderby_array as $i => $orderby ) {
 				// Only allow certain values for safety
-				$orderby = $orderby_array[$i];
+				if ( ! in_array($orderby, $allowed_keys) )
+					continue;
+
 				switch ($orderby) {
 					case 'menu_order':
 						break;
@@ -2044,15 +2046,19 @@
 					case 'meta_value':
 						$orderby = "$wpdb->postmeta.meta_value";
 						break;
+					case 'meta_value_num':
+						$orderby = "$wpdb->postmeta.meta_value+0";
+						break;
 					case 'comment_count':
 						$orderby = "$wpdb->posts.comment_count";
 						break;
 					default:
 						$orderby = "$wpdb->posts.post_" . $orderby;
 				}
-				if ( in_array($orderby_array[$i], $allowed_keys) )
-					$q['orderby'] .= (($i == 0) ? '' : ',') . $orderby;
+
+				$q['orderby'] .= (($i == 0) ? '' : ',') . $orderby;
 			}
+
 			// append ASC or DESC at the end
 			if ( !empty($q['orderby']))
 				$q['orderby'] .= " {$q['order']}";