diff --git a/libsrc/core/type_traits.hpp b/libsrc/core/type_traits.hpp
index b77a612e..894a5d07 100644
--- a/libsrc/core/type_traits.hpp
+++ b/libsrc/core/type_traits.hpp
@@ -1,4 +1,5 @@
-
+#ifndef NGS_TYPE_TRAITS_HPP
+#define NGS_TYPE_TRAITS_HPP
 
 namespace ngcore
 {
@@ -6,3 +7,5 @@ namespace ngcore
   template<bool ... vals>
   constexpr bool all_of_tmpl = std::is_same<_BoolArray<vals...>, _BoolArray<(vals || true)...>>::value;
 }
+
+#endif // NGS_TYPE_TRAITS_HPP
diff --git a/libsrc/core/version.hpp b/libsrc/core/version.hpp
index 81932695..152dbe1a 100644
--- a/libsrc/core/version.hpp
+++ b/libsrc/core/version.hpp
@@ -1,3 +1,5 @@
+#ifndef NGS_VERSION_HPP
+#define NGS_VERSION_HPP
 
 namespace ngcore
 {
@@ -82,3 +84,4 @@ namespace ngcore
     }
   };
 }
+#endif // NGS_VERSION_HPP