diff --git a/tileserver.php b/tileserver.php
index b124db1..c8b01f5 100644
--- a/tileserver.php
+++ b/tileserver.php
@@ -764,7 +764,7 @@ class Wmts extends Server {
       $profile = $m['profile'];
       $bounds = $m['bounds'];
       $format = $m['format'];
-      $mime = ($format == 'jpg') ? 'image/jpeg' : 'image/png';
+      $mime = ($format == 'jpg') ? 'image/jpeg' : 'image/' . $format;
       if ($profile == 'geodetic') {
         $tileMatrixSet = "WGS84";
       } else {