diff -Nupr a/OutputPage.php b/OutputPage.php
--- a/OutputPage.php	2020-03-31 17:45:08.074223041 +0200
+++ b/OutputPage.php	2020-03-31 17:50:46.529391505 +0200
@@ -2735,6 +2735,7 @@ class OutputPage extends ContextSource {
 			$this->prepareErrorPage( $this->msg( 'permissionserrors' ) );
 			$this->addWikiTextAsInterface( $this->formatPermissionsErrorMessage( $errors, $action ) );
 		}
+		$this->setStatusCode(403);
 	}
 
 	/**