diff --git a/lib/ajax/service.php b/lib/ajax/service.php
index 46218adf3a368..469067a3b03c3 100644
--- a/lib/ajax/service.php
+++ b/lib/ajax/service.php
@@ -115,4 +115,5 @@
     header('Accept-Ranges: none');
 }
 
+header('Content-Type: application/json; charset=utf-8');
 echo json_encode($responses);