diff --git a/include/fmt/core.h b/include/fmt/core.h
index 98c5316c..3f5e7307 100644
--- a/include/fmt/core.h
+++ b/include/fmt/core.h
@@ -629,12 +629,19 @@ inline typename std::enable_if<
 
 template <typename C, typename T, typename Char = typename C::char_type>
 inline typename std::enable_if<
+    !std::is_same<decltype(sizeof(&T::toString)), size_t>::value &&
     !convert_to_int<T, Char>::value &&
     !std::is_convertible<T, basic_string_view<Char>>::value &&
     !std::is_convertible<T, std::basic_string<Char>>::value,
     typed_value<C, custom_type>>::type
   make_value(const T &val) { return val; }
 
+template <typename C, typename T>
+inline typename std::enable_if<
+    std::is_same<decltype(sizeof(&T::toString)), size_t>::value,
+    typed_value<C, string_type>>::type
+  make_value(const T& val) {return static_cast<basic_string_view<typename C::char_type>>(val.toString());}
+
 template <typename C, typename T>
 typed_value<C, name_arg_type>
     make_value(const named_arg<T, typename C::char_type> &val) {