diff --git a/src/core/include/mp-units/ostream.h b/src/core/include/mp-units/ostream.h
index e2464bd7..d9ba6e5d 100644
--- a/src/core/include/mp-units/ostream.h
+++ b/src/core/include/mp-units/ostream.h
@@ -89,9 +89,12 @@ std::basic_ostream<CharT, Traits>& to_stream(std::basic_ostream<CharT, Traits>&
 
 MP_UNITS_EXPORT_BEGIN
 
+template<typename OStream, typename T>
+concept is_mp_units_stream = requires (OStream os, T v) { detail::to_stream_impl(os, v); }; 
+
 template<typename CharT, typename Traits, typename T>
 std::basic_ostream<CharT, Traits>& operator<<(std::basic_ostream<CharT, Traits>& os, const T& v)
-  requires requires { detail::to_stream_impl(os, v); }
+  requires is_mp_units_stream<std::basic_ostream<CharT, Traits>, T>
 {
   return detail::to_stream(os, v);
 }