diff --git a/http/server_sent_event.hpp b/http/server_sent_event.hpp
index cfc5dfb..76d10c0 100644
--- a/http/server_sent_event.hpp
+++ b/http/server_sent_event.hpp
@@ -1,4 +1,5 @@
 #pragma once
+#include "boost_formatters.hpp"
 #include "http_body.hpp"
 #include "http_request.hpp"
 #include "http_response.hpp"