1 files changed, 5 insertions, 0 deletions
diff --git a/option.h b/option.h
index 47a0624..a3ad60a 100644
--- a/option.h
+++ b/option.h
@@ -1,3 +1,6 @@
+#ifndef UTILS_OPTION_H
+#define UTILS_OPTION_H
+
 #include <cassert>
 #include <new>  // placement new
 #include <type_traits>
@@ -141,3 +144,5 @@ struct option {
   bool m_has_value{false};
 };
 }  // namespace option
+
+#endif