From 74ad0f6f68b4c2ce9abaaf73dced8c67f0bcb418 Mon Sep 17 00:00:00 2001
From: Mateusz Pusz <mateusz.pusz@gmail.com>
Date: Tue, 13 Jun 2023 17:34:37 +0300
Subject: [PATCH] fix: more constraints added to `ReferenceOf` to provide
 support for corner cases of dimensionless quantity tree

---
 src/core/include/mp-units/bits/reference_concepts.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/core/include/mp-units/bits/reference_concepts.h b/src/core/include/mp-units/bits/reference_concepts.h
index 61cd917d..c51d2d59 100644
--- a/src/core/include/mp-units/bits/reference_concepts.h
+++ b/src/core/include/mp-units/bits/reference_concepts.h
@@ -74,6 +74,9 @@ template<typename T, auto V>
 concept ReferenceOf =
   Reference<T> &&
   ((Dimension<std::remove_const_t<decltype(V)>> && get_quantity_spec(T{}).dimension == V) ||
-   (QuantitySpec<std::remove_const_t<decltype(V)>> && implicitly_convertible(get_quantity_spec(T{}), V)));
+   (QuantitySpec<std::remove_const_t<decltype(V)>> && implicitly_convertible(get_quantity_spec(T{}), V) &&
+    !detail::DerivedFromQuantityKindSpecOf<get_quantity_spec(T{}), V> &&
+    (detail::QuantityKindSpec<std::remove_const_t<decltype(get_quantity_spec(T{}))>> ||
+     !detail::DerivedFromQuantityKindSpecOf<V, get_quantity_spec(T{})>)));
 
 }  // namespace mp_units