diff --git a/libstdc++-v3/include/std/expected b/libstdc++-v3/include/std/expected
index 591fc72a4388..a03a7d3f722f 100644
--- a/libstdc++-v3/include/std/expected
+++ b/libstdc++-v3/include/std/expected
@@ -1163,15 +1163,17 @@ namespace __expected
 	    { __t == __u } -> convertible_to<bool>;
 	    { __e == __e2 } -> convertible_to<bool>;
 	  }
+	[[nodiscard]]
 	friend constexpr bool
 	operator==(const expected& __x, const expected<_Up, _Er2>& __y)
 	noexcept(noexcept(bool(*__x == *__y))
 		  && noexcept(bool(__x.error() == __y.error())))
 	{
+	  if (__x.has_value() != __y.has_value())
+	    return false;
 	  if (__x.has_value())
-	    return __y.has_value() && bool(*__x == *__y);
-	  else
-	    return !__y.has_value() && bool(__x.error() == __y.error());
+	    return *__x == *__y;
+	  return __x.error() == __y.error();
 	}
 
       template<typename _Up, same_as<_Tp> _Vp>
@@ -1179,19 +1181,29 @@ namespace __expected
 	  && requires (const _Tp& __t, const _Up& __u) {
 	    { __t == __u } -> convertible_to<bool>;
 	  }
+	[[nodiscard]]
 	friend constexpr bool
 	operator==(const expected<_Vp, _Er>& __x, const _Up& __v)
 	noexcept(noexcept(bool(*__x == __v)))
-	{ return __x.has_value() && bool(*__x == __v); }
+	{
+	  if (__x.has_value())
+	    return *__x == __v;
+	  return false;
+	}
 
       template<typename _Er2>
 	requires requires (const _Er& __e, const _Er2& __e2) {
 	  { __e == __e2 } -> convertible_to<bool>;
 	}
+	[[nodiscard]]
 	friend constexpr bool
 	operator==(const expected& __x, const unexpected<_Er2>& __e)
 	noexcept(noexcept(bool(__x.error() == __e.error())))
-	{ return !__x.has_value() && bool(__x.error() == __e.error()); }
+	{
+	  if (!__x.has_value())
+	    return __x.error() == __e.error();
+	  return false;
+	}
 
       friend constexpr void
       swap(expected& __x, expected& __y)
@@ -1841,24 +1853,31 @@ namespace __expected
 	  && requires (const _Er& __e, const _Er2& __e2) {
 	    { __e == __e2 } -> convertible_to<bool>;
 	  }
+	[[nodiscard]]
 	friend constexpr bool
 	operator==(const expected& __x, const expected<_Up, _Er2>& __y)
 	noexcept(noexcept(bool(__x.error() == __y.error())))
 	{
+	  if (__x.has_value() != __y.has_value())
+	    return false;
 	  if (__x.has_value())
-	    return __y.has_value();
-	  else
-	    return !__y.has_value() && bool(__x.error() == __y.error());
+	    return true;
+	  return __x.error() == __y.error();
 	}
 
       template<typename _Er2>
 	requires requires (const _Er& __e, const _Er2& __e2) {
 	  { __e == __e2 } -> convertible_to<bool>;
 	}
+	[[nodiscard]]
 	friend constexpr bool
 	operator==(const expected& __x, const unexpected<_Er2>& __e)
 	noexcept(noexcept(bool(__x.error() == __e.error())))
-	{ return !__x.has_value() && bool(__x.error() == __e.error()); }
+	{
+	  if (!__x.has_value())
+	    return __x.error() == __e.error();
+	  return false;
+	}
 
       friend constexpr void
       swap(expected& __x, expected& __y)
diff --git a/libstdc++-v3/testsuite/20_util/expected/equality.cc b/libstdc++-v3/testsuite/20_util/expected/equality.cc
index db19b1510a73..cc122f469082 100644
--- a/libstdc++-v3/testsuite/20_util/expected/equality.cc
+++ b/libstdc++-v3/testsuite/20_util/expected/equality.cc
@@ -28,19 +28,45 @@ test_eq()
   std::expected<int, int> e2;
   VERIFY(e2 == e2);
   VERIFY(e1 == e2);
+  VERIFY(e2 == e1);
   VERIFY(e1 != std::unexpected<int>(1));
+
   e1 = std::unexpected<int>(1);
   VERIFY(e1 == std::unexpected<int>(1));
   VERIFY(e1 != std::unexpected<int>(2));
   VERIFY(e1 != e2);
+  VERIFY(e2 != e1);
+  VERIFY(e1 != 1);
+
+  e2 = std::unexpected<int>(1);
+  VERIFY(e1 == e2);
+  VERIFY(e2 == e1);
+
+  e2 = std::unexpected<int>(2);
+  VERIFY(e1 != e2);
+  VERIFY(e2 != e1);
 
   std::expected<void, int> e3;
   VERIFY(e3 == e3);
   VERIFY(e3 != std::unexpected<int>(1));
+  std::expected<const void, long> e4;
+  VERIFY(e3 == e4);
+  VERIFY(e4 == e3);
+
   e3 = std::unexpected<int>(1);
   VERIFY(e3 == e3);
   VERIFY(e3 == std::unexpected<int>(1));
   VERIFY(e3 != std::unexpected<int>(2));
+  VERIFY(e3 != e4);
+  VERIFY(e4 != e3);
+
+  e4 = e3;
+  VERIFY(e3 == e4);
+  VERIFY(e4 == e3);
+
+  e4 = std::unexpected<int>(4);
+  VERIFY(e3 != e4);
+  VERIFY(e4 != e3);
 
   return true;
 }
diff --git a/libstdc++-v3/testsuite/20_util/expected/lwg4366.cc b/libstdc++-v3/testsuite/20_util/expected/lwg4366.cc
new file mode 100644
index 000000000000..35d53714f036
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/expected/lwg4366.cc
@@ -0,0 +1,33 @@
+// { dg-do run { target c++23 } }
+
+// LWG 4366. Heterogeneous comparison of expected may be ill-formed
+
+#include <expected>
+#include <testsuite_hooks.h>
+
+struct Bool
+{
+  operator bool() const { return true; }
+  explicit operator bool() { throw; }
+};
+
+struct E1 {
+  friend Bool operator==(E1, E1) { return {}; }
+} e1;
+
+struct E2 {
+  friend Bool operator==(E1, E2) { return {}; }
+} e2;
+
+int main()
+{
+  std::expected<int, E1> u1(std::unexpect, e1);
+  VERIFY(u1 == u1);
+
+  std::unexpected<E2> u2(e2);
+  VERIFY(u1 == u2);
+
+  std::expected<void, E1> u3(std::unexpect, e1);
+  VERIFY(u3 == u3);
+  VERIFY(u3 == u2);
+}