diff --git a/tests/t00056/t00056.cc b/tests/t00056/t00056.cc
index 92d982de..5f708867 100644
--- a/tests/t00056/t00056.cc
+++ b/tests/t00056/t00056.cc
@@ -1,3 +1,4 @@
+#include <concepts>
 #include <string>
 
 namespace clanguml {