diff --git a/src/slic3r/GUI/GUI_App.cpp b/src/slic3r/GUI/GUI_App.cpp
index 0b2244d65..c35985f11 100644
--- a/src/slic3r/GUI/GUI_App.cpp
+++ b/src/slic3r/GUI/GUI_App.cpp
@@ -53,6 +53,7 @@
 
 #if ENABLE_THUMBNAIL_GENERATOR
 #include <boost/beast/core/detail/base64.hpp>
+#include <boost/nowide/fstream.hpp>
 #endif // ENABLE_THUMBNAIL_GENERATOR
 
 namespace Slic3r {