diff --git a/include/base64.hpp b/include/base64.hpp
index 3bd61c8..4094edb 100644
--- a/include/base64.hpp
+++ b/include/base64.hpp
@@ -9,6 +9,7 @@
 #include <stdexcept>
 #include <string>
 #include <string_view>
+#include <type_traits>
 
 #if defined(__cpp_lib_bit_cast)
 #include <bit>  // For std::bit_cast.