diff --git a/src/slic3r/GUI/Gizmos/GLGizmoSimplify.cpp b/src/slic3r/GUI/Gizmos/GLGizmoSimplify.cpp
index 9f5990e23..90b601a9d 100644
--- a/src/slic3r/GUI/Gizmos/GLGizmoSimplify.cpp
+++ b/src/slic3r/GUI/Gizmos/GLGizmoSimplify.cpp
@@ -5,6 +5,7 @@
 #include "slic3r/GUI/GUI_ObjectList.hpp"
 #include "slic3r/GUI/NotificationManager.hpp"
 #include "slic3r/GUI/Plater.hpp"
+#include "slic3r/GUI/format.hpp"
 #include "libslic3r/AppConfig.hpp"
 #include "libslic3r/Model.hpp"
 #include "libslic3r/QuadricEdgeCollapse.hpp"