diff --git a/include/linear_feedback_controller/time.hpp b/include/linear_feedback_controller/time.hpp
index ace7f5d..1b9c7f0 100644
--- a/include/linear_feedback_controller/time.hpp
+++ b/include/linear_feedback_controller/time.hpp
@@ -1,3 +1,6 @@
+#ifndef LINEAR_FEEDBACK_CONTROLLER__TIME_HPP_
+#define LINEAR_FEEDBACK_CONTROLLER__TIME_HPP_
+
 #include <chrono>
 
 namespace linear_feedback_controller {
@@ -6,3 +9,5 @@ using TimePoint = std::chrono::time_point<std::chrono::high_resolution_clock,
 
 using Duration = std::chrono::duration<double>;
 }  // namespace linear_feedback_controller
+
+#endif