diff --git a/src/slic3r/GUI/GLModel.hpp b/src/slic3r/GUI/GLModel.hpp
index 1258da1cb6..f2fc9da9b3 100644
--- a/src/slic3r/GUI/GLModel.hpp
+++ b/src/slic3r/GUI/GLModel.hpp
@@ -6,6 +6,8 @@
 #include <vector>
 #include <string>
 
+struct indexed_triangle_set;
+
 namespace Slic3r {
 
 class TriangleMesh;