diff --git a/classes/core/PKPString.php b/classes/core/PKPString.php
index 68ad9fc6ca3..da0060a8823 100644
--- a/classes/core/PKPString.php
+++ b/classes/core/PKPString.php
@@ -377,6 +377,7 @@ public static function getAmbiguousExtensionsMap()
     {
         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',