--- CRM/Report/Form/Activity.php.orig
+++ CRM/Report/Form/Activity.php
@@ -222,6 +222,16 @@
           ),
         ),
       ),
+      'civicrm_case_activity' => array(
+        'dao' => 'CRM_Case_DAO_CaseActivity',
+        'fields' => array(
+          'case_id' => array(
+            'name' => 'case_id',
+            'title' => ts('Case ID'),
+            'type' => CRM_Utils_Type::T_INT,
+          ),
+        ),
+      ),
       'civicrm_activity' => array(
         'dao' => 'CRM_Activity_DAO_Activity',
         'fields' => array(
@@ -524,6 +534,8 @@
                      {$this->_aliases['civicrm_activity_contact']}.record_type_id = {$targetID}
            INNER JOIN civicrm_contact civicrm_contact_target
                   ON {$this->_aliases['civicrm_activity_contact']}.contact_id = civicrm_contact_target.id
+           LEFT JOIN civicrm_case_activity {$this->_aliases['civicrm_case_activity']}
+                  ON {$this->_aliases['civicrm_activity']}.id = {$this->_aliases['civicrm_case_activity']}.activity_id
            {$this->_aclFrom}";

     if ($this->isTableSelected('civicrm_email')) {
@@ -852,6 +864,8 @@
       INNER JOIN civicrm_activity_contact {$this->_aliases['civicrm_activity_contact']} ON {$this->_aliases['civicrm_activity_contact']}.activity_id
_aliases['civicrm_activity']}.id
       AND {$this->_aliases['civicrm_activity_contact']}.record_type_id = {$sourceID}
       LEFT JOIN civicrm_contact contact_civireport ON contact_civireport.id = {$this->_aliases['civicrm_activity_contact']}.contact_id
+      LEFT JOIN civicrm_case_activity {$this->_aliases['civicrm_case_activity']}
+        ON {$this->_aliases['civicrm_activity']}.id = {$this->_aliases['civicrm_case_activity']}.activity_id
       {$this->_where} {$groupByFromSelect} {$this->_having} {$this->_orderBy} {$this->_limit}";

     CRM_Utils_Hook::alterReportVar('sql', $this, $this);
@@ -1131,6 +1145,8 @@
                        {$this->_aliases['civicrm_activity_contact']}.record_type_id = {$assigneeID}
              INNER JOIN civicrm_contact civicrm_contact_assignee
                     ON {$this->_aliases['civicrm_activity_contact']}.contact_id = civicrm_contact_assignee.id
+           LEFT JOIN civicrm_case_activity {$this->_aliases['civicrm_case_activity']}
+                  ON {$this->_aliases['civicrm_activity']}.id = {$this->_aliases['civicrm_case_activity']}.activity_id
              {$this->_aclFrom}";

     if ($this->isTableSelected('civicrm_email')) {
@@ -1165,6 +1181,8 @@
                        {$this->_aliases['civicrm_activity_contact']}.record_type_id = {$sourceID}
              INNER JOIN civicrm_contact civicrm_contact_source
                     ON {$this->_aliases['civicrm_activity_contact']}.contact_id = civicrm_contact_source.id
+           LEFT JOIN civicrm_case_activity {$this->_aliases['civicrm_case_activity']}
+                  ON {$this->_aliases['civicrm_activity']}.id = {$this->_aliases['civicrm_case_activity']}.activity_id
              {$this->_aclFrom}";

     if ($this->isTableSelected('civicrm_email')) {