diff --git a/test/core/core_force_cxx_unknown.cpp b/test/core/core_force_cxx_unknown.cpp
index 61c5190c..62299d6a 100644
--- a/test/core/core_force_cxx_unknown.cpp
+++ b/test/core/core_force_cxx_unknown.cpp
@@ -1,4 +1,6 @@
-#define GLM_FORCE_CXX_UNKNOWN
+#ifndef GLM_FORCE_CXX_UNKNOWN
+#	define GLM_FORCE_CXX_UNKNOWN
+#endif
 
 #include <glm/glm.hpp>
 #include <glm/ext.hpp>