diff --git a/include/utempl/constexpr_string.hpp b/include/utempl/constexpr_string.hpp
index cfb88d0..0d0d939 100644
--- a/include/utempl/constexpr_string.hpp
+++ b/include/utempl/constexpr_string.hpp
@@ -1,5 +1,6 @@
 #pragma once
 #include <fmt/format.h>
+#include <algorithm>
 
 namespace utempl {
 template <std::size_t>