diff --git a/app/code/core/Mage/Core/Block/Abstract.php b/app/code/core/Mage/Core/Block/Abstract.php
index f565235a356..edaedb2444a 100644
--- a/app/code/core/Mage/Core/Block/Abstract.php
+++ b/app/code/core/Mage/Core/Block/Abstract.php
@@ -755,6 +755,7 @@ public function insert($block, $siblingName = '', $after = false, $alias = '')
      */
     public function sortChildren($force = false)
     {
+        $this->_sortedChildren = array_values($this->_sortedChildren); // reset indexes which might have gaps after unsetting blocks
         foreach ($this->_sortInstructions as $name => $list) {
             list($siblingName, $after, $exists) = $list;
             if ($exists && !$force) {