diff --git a/include/xlnt/utils/optional.hpp b/include/xlnt/utils/optional.hpp
index 27a6e6b9..ab9c9a7d 100644
--- a/include/xlnt/utils/optional.hpp
+++ b/include/xlnt/utils/optional.hpp
@@ -27,6 +27,7 @@
 #include "xlnt/utils/numeric.hpp"
 #include "xlnt/xlnt_config.hpp"
 #include <type_traits>
+#include <memory>
 
 namespace xlnt {