diff --git a/include/experimental/__p0009_bits/layout_left.hpp b/include/experimental/__p0009_bits/layout_left.hpp
index c6dc1d19..0248f586 100644
--- a/include/experimental/__p0009_bits/layout_left.hpp
+++ b/include/experimental/__p0009_bits/layout_left.hpp
@@ -132,6 +132,7 @@ class layout_left::mapping {
       )
     )
     MDSPAN_CONDITIONAL_EXPLICIT((!std::is_convertible_v<typename _Mapping::extents_type, extents_type>))
+    MDSPAN_INLINE_FUNCTION constexpr
     mapping(const _Mapping& __other) noexcept
       : __extents(__other.extents())
     {
diff --git a/include/experimental/__p0009_bits/layout_right.hpp b/include/experimental/__p0009_bits/layout_right.hpp
index 93de9f47..04f1b640 100644
--- a/include/experimental/__p0009_bits/layout_right.hpp
+++ b/include/experimental/__p0009_bits/layout_right.hpp
@@ -132,6 +132,7 @@ class layout_right::mapping {
         MDSPAN_IMPL_PROPOSED_NAMESPACE::detail::is_layout_right_padded_mapping<_Mapping>::value
         && std::is_constructible_v<extents_type, typename _Mapping::extents_type>))
     MDSPAN_CONDITIONAL_EXPLICIT((!std::is_convertible_v<typename _Mapping::extents_type, extents_type>))
+    MDSPAN_INLINE_FUNCTION constexpr
     mapping(const _Mapping &__other) noexcept
         : __extents(__other.extents())
     {