diff --git misc/tabledrag.js misc/tabledrag.js
index cd28f14..99bdf6f 100644
--- misc/tabledrag.js
+++ misc/tabledrag.js
@@ -998,7 +998,7 @@ Drupal.tableDrag.prototype.row.prototype.findSiblings = function (rowSettings) {
   var siblings = [];
   var directions = ['prev', 'next'];
   var rowIndentation = this.indents;
-  for (var d in directions) {
+  for (var d = 0; d < directions.length; d++) {
     var checkRow = $(this.element)[directions[d]]();
     while (checkRow.length) {
       // Check that the sibling contains a similar target field.