diff --git a/classes/core/PKPString.php b/classes/core/PKPString.php
index 1260a5234df..106008290f3 100644
--- a/classes/core/PKPString.php
+++ b/classes/core/PKPString.php
@@ -131,6 +131,7 @@ public static function getAmbiguousExtensionsMap(): array
     {
         return [
             'html:text/xml' => 'text/html',
+            'xhtml:text/xml' => 'text/html',
             'css:text/x-c' => 'text/css',
             'css:text/plain' => 'text/css',
             'csv:text/plain' => 'text/csv',