diff --git a/mitama/app/__init__.py b/mitama/app/__init__.py
index ba2662a..0596beb 100644
--- a/mitama/app/__init__.py
+++ b/mitama/app/__init__.py
@@ -85,11 +85,9 @@ def handle(self, req: Request):
             for path in self.paths:
                 filename = path / req.params['path']
                 if filename.is_file():
-                    mime = guess_type(str(filename)) or 'application/octet-stream'
+                    mime = guess_type(str(filename)) or ('application/octet-stream', )
                     with open(filename, 'rb') as f:
-                        return Response(body = f.read(), headers={
-                            'content-type': mime[0]
-                        })
+                        return Response(body = f.read(), content_type = mime[0])
             for path in self.paths:
                 filename = path / '404.html'
                 if filename.is_file():