diff --git a/src/libslic3r/Config.hpp b/src/libslic3r/Config.hpp
index 5a6c54f14..736b24400 100644
--- a/src/libslic3r/Config.hpp
+++ b/src/libslic3r/Config.hpp
@@ -1479,7 +1479,7 @@ public:
         	unsigned char new_value = 0;
         	if (item_str == "nil") {
         		if (NULLABLE)
-        			this->values.push_back(nil_value());
+                    new_value = nil_value();
         		else
                     throw ConfigurationError("Deserializing nil into a non-nullable object");
         	} else if (item_str == "1") {
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 {