diff --git a/include/fmt/core.h b/include/fmt/core.h
index 3f5e7307..c711df70 100644
--- a/include/fmt/core.h
+++ b/include/fmt/core.h
@@ -629,7 +629,6 @@ 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,
@@ -640,7 +639,7 @@ 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());}
+  make_value(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>