diff --git a/core/modules/block/js/block.js b/core/modules/block/js/block.js
index 0bd99df..c133c0c 100644
--- a/core/modules/block/js/block.js
+++ b/core/modules/block/js/block.js
@@ -110,7 +110,7 @@
           var select = $(this);
 
           // Find the correct region and insert the row as the last in the region.
-          table.find('.region-' + select[0].value + '-message').nextUntil('.region-message').last().before(row);
+          table.find('.region-' + select[0].value + '-message').nextUntil('.region-message').eq(-1).before(row);
 
           // Update the block weights
           updateBlockweights(table, select[0].value);