--- a/common.h
+++ b/common.h
@@ -38,6 +38,11 @@
 using nonstd::optional;
 using nonstd::nullopt;
 using nonstd::make_optional;
+#else
+#include <optional>
+using std::optional;
+using std::nullopt;
+using std::make_optional;
 #endif
 #endif