diff --git a/src/test/test_data.hpp b/src/test/test_data.hpp
index 20a4b90ef..61a4e9748 100644
--- a/src/test/test_data.hpp
+++ b/src/test/test_data.hpp
@@ -1,4 +1,5 @@
 #ifndef SLIC3R_TEST_DATA_HPP
+#define SLIC3R_TEST_DATA_HPP
 #include "Point.hpp"
 #include "TriangleMesh.hpp"
 #include "Geometry.hpp"