diff --git a/libraries/classes/Controllers/ExportController.php b/libraries/classes/Controllers/ExportController.php
index 25da87ab76..ee616f2d83 100644
--- a/libraries/classes/Controllers/ExportController.php
+++ b/libraries/classes/Controllers/ExportController.php
@@ -260,7 +260,7 @@ final class ExportController extends AbstractController
             $quick_export = false;
         }
 
-        if ($_POST['output_format'] === 'astext') {
+        if (isset($_POST['output_format']) && $_POST['output_format'] === 'astext') {
             $asfile = false;
         } else {
             $asfile = true;