diff --git a/CRM/DataprocessorSearch/Form/Search.php b/CRM/DataprocessorSearch/Form/Search.php
index 1234d22a523ba4500518d494cd656648958c059e..e368e53dc5b436b3219f166b3f4a35b47071677d 100644
--- a/CRM/DataprocessorSearch/Form/Search.php
+++ b/CRM/DataprocessorSearch/Form/Search.php
@@ -160,7 +160,7 @@ class CRM_DataprocessorSearch_Form_Search extends CRM_DataprocessorSearch_Form_A
    */
   protected function alterDataProcessor(\Civi\DataProcessor\ProcessorType\AbstractProcessorType $dataProcessorClass) {
     if (isset($this->dataProcessorOutput['configuration']['expose_aggregate']) && $this->dataProcessorOutput['configuration']['expose_aggregate']) {
-      $aggregateFields = $this->_formValues['aggregateFields'];
+      $aggregateFields = isset($this->_formValues['aggregateFields']) ? $this->_formValues['aggregateFields'] : array();
       foreach ($this->dataProcessorClass->getDataFlow()->getOutputFieldHandlers() as $outputFieldHandler) {
         if ($outputFieldHandler instanceof \Civi\DataProcessor\FieldOutputHandler\OutputHandlerAggregate) {
           $alias = $outputFieldHandler->getAggregateFieldSpec()->alias;