diff --git a/ao.php b/ao.php
index 2beb6fe1d6322afe3062954b22d5ca4205ccb6f5..5d4fb2fd87e1a70c0c8653339a910d47c33aaf2c 100644
--- a/ao.php
+++ b/ao.php
@@ -111,7 +111,11 @@ function ao_civicrm_validateForm($formName, &$fields, &$files, &$form, &$errors)
         }
       } */
       if (!empty($assigneeContact)) {
-        $isAoEmail = CRM_Core_DAO::singleValueQuery("SELECT 1 FROM civicrm_email WHERE email LIKE '%@autismontario.com' AND contact_id = $assigneeContact LIMIT 1");
+        $op = '=';
+        if (strpos($assigneeContact, ',') !== FALSE) {
+          $op = 'IN';
+        }
+        $isAoEmail = CRM_Core_DAO::singleValueQuery("SELECT 1 FROM civicrm_email WHERE email LIKE '%@autismontario.com' AND contact_id {$op} {$assigneeContact} LIMIT 1");
         if (!$isAoEmail) {
           $errors['assignee_contact_id'] = ts('The contact being assigned to this activity must be an AO staff member');
         }