diff --git a/src/libslic3r/Optimize/Optimizer.hpp b/src/libslic3r/Optimize/Optimizer.hpp
index 05191eba2..8ae55c61c 100644
--- a/src/libslic3r/Optimize/Optimizer.hpp
+++ b/src/libslic3r/Optimize/Optimizer.hpp
@@ -8,6 +8,7 @@
 #include <functional>
 #include <limits>
 #include <cassert>
+#include <optional>
 
 namespace Slic3r { namespace opt {