diff --git a/include/fmt/core.h b/include/fmt/core.h
index 0d7d15b5..c8b987af 100644
--- a/include/fmt/core.h
+++ b/include/fmt/core.h
@@ -1409,7 +1409,8 @@ inline std::basic_string<Char> vformat(
 */
 // Pass char_t as a default template parameter instead of using
 // std::basic_string<char_t<S>> to reduce the symbol size.
-template <typename S, typename... Args, typename Char = char_t<S>>
+template <typename S, typename... Args, typename Char = char_t<S>,
+          FMT_ENABLE_IF(internal::is_string<S>::value)>
 inline std::basic_string<Char> format(const S& format_str, Args&&... args) {
   return internal::vformat(
       to_string_view(format_str),
diff --git a/include/fmt/format.h b/include/fmt/format.h
index e198233b..11da7a76 100644
--- a/include/fmt/format.h
+++ b/include/fmt/format.h
@@ -3351,7 +3351,8 @@ inline typename buffer_context<Char>::iterator vformat_to(
 }
 
 template <typename S, typename... Args, std::size_t SIZE = inline_buffer_size,
-          typename Char = enable_if_t<internal::is_string<S>::value, char_t<S>>>
+          typename Char = char_t<S>,
+          FMT_ENABLE_IF(internal::is_string<S>::value)>
 inline typename buffer_context<Char>::iterator format_to(
     basic_memory_buffer<Char, SIZE>& buf, const S& format_str, Args&&... args) {
   internal::check_format_string<Args...>(format_str);