Index: clang/include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -11047,7 +11047,7 @@
   "use std::%0 instead">,
   InGroup<DeprecatedExperimentalCoroutine>;
 def err_mixed_use_std_and_experimental_namespace_for_coroutine : Error<
-  "mixed use of std and std::experimental namespaces for "
+  "conflicting mixed use of std and std::experimental namespaces for "
   "coroutine components">;
 def err_implicit_coroutine_std_nothrow_type_not_found : Error<
   "std::nothrow was not found; include <new> before defining a coroutine which "
Index: clang/lib/Sema/SemaCoroutine.cpp
===================================================================
--- clang/lib/Sema/SemaCoroutine.cpp
+++ clang/lib/Sema/SemaCoroutine.cpp
@@ -1705,8 +1705,9 @@
       auto *Found = *ResExp.begin();
       Diag(Found->getLocation(), diag::note_entity_declared_at) << Found;
 
-      if (InStd) {
-        // Also found in std
+      if (InStd &&
+          StdCoroutineTraitsCache != ResExp.getAsSingle<ClassTemplateDecl>()) {
+        // Also found something different in std
         Diag(KwLoc,
              diag::err_mixed_use_std_and_experimental_namespace_for_coroutine);
         Diag(StdCoroutineTraitsCache->getLocation(),
Index: clang/test/SemaCXX/coroutine-mixed3-exp-namespace.cpp
===================================================================
--- /dev/null
+++ clang/test/SemaCXX/coroutine-mixed3-exp-namespace.cpp
@@ -0,0 +1,31 @@
+// RUN: %clang_cc1 -verify -std=c++20 -fsyntax-only %s
+
+#include "Inputs/std-coroutine.h"
+
+namespace std::experimental {
+// expected-note@+1{{declared here}}
+using std::coroutine_handle;
+using std::coroutine_traits;
+} // namespace std::experimental
+
+struct my_awaitable {
+  bool await_ready() noexcept;
+  void await_suspend(std::coroutine_handle<> coro) noexcept;
+  void await_resume() noexcept;
+};
+
+struct promise_void {
+  void get_return_object();
+  my_awaitable initial_suspend();
+  my_awaitable final_suspend() noexcept;
+  void return_void();
+  void unhandled_exception();
+};
+
+template <>
+struct std::coroutine_traits<void> { using promise_type = promise_void; };
+
+void test() {
+  co_return;
+  // expected-warning@-1{{support for std::experimental::coroutine_traits will be removed}}
+}
Index: clang/test/SemaCXX/coroutine-mixed4-exp-namespace.cpp
===================================================================
--- /dev/null
+++ clang/test/SemaCXX/coroutine-mixed4-exp-namespace.cpp
@@ -0,0 +1,31 @@
+// RUN: %clang_cc1 -verify=expected,declared -std=c++20 -fsyntax-only %s
+
+#include "Inputs/std-coroutine.h" // First
+
+namespace std::experimental {
+// expected-note@+1{{declared here}}
+template <typename T> using coroutine_traits = std::coroutine_traits<T>;
+using std::coroutine_handle;
+} // namespace std::experimental
+
+struct my_awaitable {
+  bool await_ready() noexcept;
+  void await_suspend(std::experimental::coroutine_handle<> coro) noexcept;
+  void await_resume() noexcept;
+};
+
+struct promise_void {
+  void get_return_object();
+  my_awaitable initial_suspend();
+  my_awaitable final_suspend() noexcept;
+  void return_void();
+  void unhandled_exception();
+};
+
+template <>
+struct std::coroutine_traits<void> { using promise_type = promise_void; };
+
+void test() {
+  co_return; // expected-error {{mixed use of std and std::experimental namespaces for coroutine components}}
+  // expected-warning@-1{{support for std::experimental::coroutine_traits will be removed}}
+}