diff --git a/http/mutual_tls.hpp b/http/mutual_tls.hpp
index 1620054..9f9f82b 100644
--- a/http/mutual_tls.hpp
+++ b/http/mutual_tls.hpp
@@ -4,8 +4,11 @@
 #include "mutual_tls_meta.hpp"
 #include "persistent_data.hpp"
 
+extern "C"
+{
 #include <openssl/crypto.h>
 #include <openssl/ssl.h>
+}
 
 #include <boost/asio/ip/address.hpp>
 #include <boost/asio/ssl/verify_context.hpp>