diff --git a/SimoxUtility/meta/undefined_t/is_set.h b/SimoxUtility/meta/undefined_t/is_set.h
index 7221f5c9115f35452613dcfa9c17c6aefe6d739e..af0e74dfdc9105bdac4179b4f6dadbf3eb2e1924 100644
--- a/SimoxUtility/meta/undefined_t/is_set.h
+++ b/SimoxUtility/meta/undefined_t/is_set.h
@@ -2,6 +2,8 @@
 
 #include "undefined_t.h"
 
+#include <array>
+
 namespace simox::meta
 {
     template<class T>