diff --git a/htdocs/caldav.php b/htdocs/caldav.php
index 812b32d7..f6ddf918 100644
--- a/htdocs/caldav.php
+++ b/htdocs/caldav.php
@@ -147,5 +147,5 @@ switch ( $request->method ) {
     dbg_error_log( 'caldav', 'RAW: %s', str_replace("\n", '',str_replace("\r", '', $request->raw_post)) );
 }
 
-$request->DoResponse( 500, translate('The application program does not understand that request.') );
+$request->DoResponse( 400, translate('The application program does not understand that request.') );