diff --git a/include/experimental/__p0009_bits/layout_left.hpp b/include/experimental/__p0009_bits/layout_left.hpp
index 2b3a9bdf..bb17c449 100644
--- a/include/experimental/__p0009_bits/layout_left.hpp
+++ b/include/experimental/__p0009_bits/layout_left.hpp
@@ -188,7 +188,7 @@ class layout_left::mapping {
     }
 
     // In C++ 20 the not equal exists if equal is found
-#if MDSPAN_HAS_CXX_20
+#if !(MDSPAN_HAS_CXX_20)
     template<class OtherExtents>
     MDSPAN_INLINE_FUNCTION
     friend constexpr bool operator!=(mapping const& lhs, mapping<OtherExtents> const& rhs) noexcept {
diff --git a/include/experimental/__p0009_bits/layout_right.hpp b/include/experimental/__p0009_bits/layout_right.hpp
index 2ab20f19..dc345806 100644
--- a/include/experimental/__p0009_bits/layout_right.hpp
+++ b/include/experimental/__p0009_bits/layout_right.hpp
@@ -190,7 +190,7 @@ class layout_right::mapping {
     }
 
     // In C++ 20 the not equal exists if equal is found
-#if MDSPAN_HAS_CXX_20
+#if !(MDSPAN_HAS_CXX_20)
     template<class OtherExtents>
     MDSPAN_INLINE_FUNCTION
     friend constexpr bool operator!=(mapping const& lhs, mapping<OtherExtents> const& rhs) noexcept {
diff --git a/tests/test_layout_ctors.cpp b/tests/test_layout_ctors.cpp
index e4e3475f..5a83a585 100644
--- a/tests/test_layout_ctors.cpp
+++ b/tests/test_layout_ctors.cpp
@@ -68,6 +68,7 @@ TYPED_TEST(TestLayoutCtors, default_ctor) {
   auto m2 = typename TestFixture::mapping_type{};
   ASSERT_EQ(m2.extents(), typename TestFixture::extents_type{});
   ASSERT_EQ(m, m2);
+  ASSERT_FALSE(m != m2);
 }
 
 template <class> struct TestLayoutCompatCtors;