diff --git a/test/controller_mock.hpp b/test/controller_mock.hpp
index 533b6db..30b7bef 100644
--- a/test/controller_mock.hpp
+++ b/test/controller_mock.hpp
@@ -4,6 +4,8 @@
 #include "pid/pidcontroller.hpp"
 #include "pid/zone_interface.hpp"
 
+#include <string>
+
 #include <gmock/gmock.h>
 
 namespace pid_control