diff --git a/h5p.classes.php b/h5p.classes.php
index fccb4de..d9b4e4b 100644
--- a/h5p.classes.php
+++ b/h5p.classes.php
@@ -2881,7 +2881,7 @@ class H5PCore {
    */
   private static function printJson($data, $status_code = NULL) {
     header('Cache-Control: no-cache');
-    header('Content-type: application/json; charset=utf-8');
+    header('Content-Type: application/json; charset=utf-8');
     print json_encode($data);
   }