Reported upstream by email to Ingo Ruhnke <grumbel@gmail.com>.

diff -u -r a/test/numeric_less_test.cpp b/test/numeric_less_test.cpp
--- a/test/numeric_less_test.cpp	2025-07-20 13:02:31.088465392 +0200
+++ b/test/numeric_less_test.cpp	2025-07-20 13:03:49.283025547 +0200
@@ -1,4 +1,5 @@
 #include <gtest/gtest.h>
+#include <algorithm>
 
 #include "strut/numeric_less.hpp"