diff --git a/CRM/Report/Form/Case/Summary.php b/CRM/Report/Form/Case/Summary.php
index 9fb57a339714..55f8490a5ec4 100644
--- a/CRM/Report/Form/Case/Summary.php
+++ b/CRM/Report/Form/Case/Summary.php
@@ -369,7 +369,8 @@ public function where() {
   }
 
   public function groupBy() {
-    $this->_groupBy = "";
+    $cc = $this->_aliases['civicrm_case'];
+    $this->_groupBy = "group by $cc.id";
   }
 
   public function postProcess() {