diff --git a/CRM/Activity/Form/Activity.php b/CRM/Activity/Form/Activity.php
index 71d6ff01956b..c56403f914a2 100644
--- a/CRM/Activity/Form/Activity.php
+++ b/CRM/Activity/Form/Activity.php
@@ -523,7 +523,9 @@ public function preProcess() {
 
     if ($this->_action & CRM_Core_Action::UPDATE) {
       // We filter out alternatives, in case this is a stored e-mail, before sending to front-end
-      $this->_values['details'] = CRM_Utils_String::stripAlternatives($this->_values['details']) ?: '';
+      if (isset($this->_values['details'])) {
+        $this->_values['details'] = CRM_Utils_String::stripAlternatives($this->_values['details']) ?: '';
+      }
 
       if ($this->_activityTypeName === 'Inbound Email' &&
         !CRM_Core_Permission::check('edit inbound email basic information and content')