diff --git a/src/libslic3r/QuadricEdgeCollapse.hpp b/src/libslic3r/QuadricEdgeCollapse.hpp
index 956ad35113..0043fc24a3 100644
--- a/src/libslic3r/QuadricEdgeCollapse.hpp
+++ b/src/libslic3r/QuadricEdgeCollapse.hpp
@@ -4,6 +4,8 @@
 // paper: https://people.eecs.berkeley.edu/~jrs/meshpapers/GarlandHeckbert2.pdf
 // sum up: https://users.csc.calpoly.edu/~zwood/teaching/csc570/final06/jseeba/
 // inspiration: https://github.com/sp4cerat/Fast-Quadric-Mesh-Simplification
+#ifndef PRUSASLICER_QUADRIC_EDGE_COLLAPSE_HPP
+#define PRUSASLICER_QUADRIC_EDGE_COLLAPSE_HPP
 
 #include <cstdint>
 #include <functional>
@@ -30,3 +32,5 @@ void its_quadric_edge_collapse(
 
 } // namespace Slic3r
 #endif // slic3r_quadric_edge_collapse_hpp_
+
+#endif // PRUSASLICER_QUADRIC_EDGE_COLLAPSE_HPP