diff --git a/interface.php b/interface.php
index cc6b863..a7b69b6 100644
--- a/interface.php
+++ b/interface.php
@@ -255,9 +255,12 @@ switch ($action) {
                     if (isset($_FILES["game_file"])) {
                         // decide weather it's a package or a plain table
                         $file = $_FILES["game_file"];
-                        $file_type = $file["type"];
                         $challenge_import_status = [];
-                        if ($file_type === "application/zip") { // a package was uploaded
+
+                        // determine MIME type
+                        $file_type = strtolower(pathinfo($file["name"], PATHINFO_EXTENSION));
+
+                        if ($file_type === "zip") { // a package was uploaded
                             $zip = new ZipArchive;
                             if ($zip->open($file["tmp_name"])) {
 
@@ -279,7 +282,7 @@ switch ($action) {
                                     $challenge_import_status = import_challenges_from_csv($csv_files[0], $gameid);
                                 }
                             }
-                        } else if ($file_type === "text/csv") { // a plain table was uploaded
+                        } else if ($file_type === "csv") { // a plain table was uploaded
                             $challenge_import_status = import_challenges_from_csv($file["tmp_name"], $gameid);
                         }
                         $result = json_encode($challenge_import_status);