diff --git a/clang/lib/Sema/SemaModule.cpp b/clang/lib/Sema/SemaModule.cpp
index 6c39cc0b44ca4..84a1fd854d804 100644
--- a/clang/lib/Sema/SemaModule.cpp
+++ b/clang/lib/Sema/SemaModule.cpp
@@ -162,7 +162,8 @@ static bool DiagReservedModuleName(Sema &S, const IdentifierInfo *II,
   case Invalid:
     return S.Diag(Loc, diag::err_invalid_module_name) << II;
   case Reserved:
-    return S.Diag(Loc, diag::warn_reserved_module_name) << II;
+    S.Diag(Loc, diag::warn_reserved_module_name) << II;
+    return false;
   }
   llvm_unreachable("fell off a fully covered switch");
 }
@@ -267,10 +268,8 @@ Sema::ActOnModuleDecl(SourceLocation StartLoc, SourceLocation ModuleLoc,
   if (!getSourceManager().isInSystemHeader(Path[0].second) &&
       (FirstComponentName == "std" ||
        (FirstComponentName.startswith("std") &&
-        llvm::all_of(FirstComponentName.drop_front(3), &llvm::isDigit)))) {
+        llvm::all_of(FirstComponentName.drop_front(3), &llvm::isDigit))))
     Diag(Path[0].second, diag::warn_reserved_module_name) << Path[0].first;
-    return nullptr;
-  }
 
   // Then test all of the components in the path to see if any of them are
   // using another kind of reserved or invalid identifier.
diff --git a/clang/test/Modules/reserved-names-1.cpp b/clang/test/Modules/reserved-names-1.cpp
deleted file mode 100644
index a92c2244f1cb6..0000000000000
--- a/clang/test/Modules/reserved-names-1.cpp
+++ /dev/null
@@ -1,46 +0,0 @@
-// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected,loud %s
-// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected -Wno-reserved-module-identifier %s
-
-// expected-note@1 15{{add 'module;' to the start of the file to introduce a global module fragment}}
-
-module std;    // loud-warning {{'std' is a reserved name for a module}}
-module _Test;  // loud-warning {{'_Test' is a reserved name for a module}} \
-                  expected-error {{module declaration must occur at the start of the translation unit}}
-module module; // expected-error {{'module' is an invalid name for a module}} \
-                  expected-error {{module declaration must occur at the start of the translation unit}}
-module std0;   // loud-warning {{'std0' is a reserved name for a module}} \
-                  expected-error {{module declaration must occur at the start of the translation unit}}
-
-export module module; // expected-error {{'module' is an invalid name for a module}} \
-                         expected-error {{module declaration must occur at the start of the translation unit}}
-export module import; // expected-error {{'import' is an invalid name for a module}} \
-                         expected-error {{module declaration must occur at the start of the translation unit}}
-export module _Test;  // loud-warning {{'_Test' is a reserved name for a module}} \
-                         expected-error {{module declaration must occur at the start of the translation unit}}
-export module __test; // loud-warning {{'__test' is a reserved name for a module}} \
-                         expected-error {{module declaration must occur at the start of the translation unit}}
-export module te__st; // loud-warning {{'te__st' is a reserved name for a module}} \
-                         expected-error {{module declaration must occur at the start of the translation unit}}
-export module std;    // loud-warning {{'std' is a reserved name for a module}} \
-                         expected-error {{module declaration must occur at the start of the translation unit}}
-export module std.foo;// loud-warning {{'std' is a reserved name for a module}} \
-                         expected-error {{module declaration must occur at the start of the translation unit}}
-export module std0;   // loud-warning {{'std0' is a reserved name for a module}} \
-                         expected-error {{module declaration must occur at the start of the translation unit}}
-export module std1000000; // loud-warning {{'std1000000' is a reserved name for a module}} \
-                         expected-error {{module declaration must occur at the start of the translation unit}}
-export module should_diag._Test; // loud-warning {{'_Test' is a reserved name for a module}} \
-                                    expected-error {{module declaration must occur at the start of the translation unit}}
-
-// Show that being in a system header doesn't save you from diagnostics about
-// use of an invalid module-name identifier.
-# 34 "reserved-names-1.cpp" 1 3
-export module module;       // expected-error {{'module' is an invalid name for a module}} \
-                               expected-error {{module declaration must occur at the start of the translation unit}}
-
-export module _Test.import; // expected-error {{'import' is an invalid name for a module}} \
-                               expected-error {{module declaration must occur at the start of the translation unit}}
-# 39 "reserved-names-1.cpp" 2 3
-
-// We can still use a reserved name on imoport.
-import std; // expected-error {{module 'std' not found}}
diff --git a/clang/test/Modules/reserved-names-1.cppm b/clang/test/Modules/reserved-names-1.cppm
new file mode 100644
index 0000000000000..e780f1e35b3b7
--- /dev/null
+++ b/clang/test/Modules/reserved-names-1.cppm
@@ -0,0 +1,154 @@
+// RUN: rm -rf %t
+// RUN: mkdir -p %t
+// RUN: split-file %s %t
+
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected,loud %t/module.cpp
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected -Wno-reserved-module-identifier %t/module.cpp
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected,loud %t/import.cpp
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected -Wno-reserved-module-identifier %t/import.cpp
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected,loud %t/_Test.cpp
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected -DNODIAGNOSTICS -Wno-reserved-module-identifier %t/_Test.cpp
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected,loud %t/__test.cpp
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected -DNODIAGNOSTICS -Wno-reserved-module-identifier %t/__test.cpp
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected,loud %t/te__st.cpp
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected -DNODIAGNOSTICS -Wno-reserved-module-identifier %t/te__st.cpp
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected,loud %t/std.cpp
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected -Wno-reserved-module-identifier %t/std.cpp
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected,loud %t/std.foo.cpp
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected -Wno-reserved-module-identifier %t/std.foo.cpp
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected,loud %t/std0.cpp
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected -Wno-reserved-module-identifier %t/std0.cpp
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected,loud %t/std1000000.cpp
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected -Wno-reserved-module-identifier %t/std1000000.cpp
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected,loud %t/module.cppm
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected -Wno-reserved-module-identifier %t/module.cppm
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected,loud %t/import.cppm
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected -Wno-reserved-module-identifier %t/import.cppm
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected,loud %t/_Test.cppm
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected -DNODIAGNOSTICS -Wno-reserved-module-identifier %t/_Test.cppm
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected,loud %t/__test.cppm
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected -DNODIAGNOSTICS -Wno-reserved-module-identifier %t/__test.cppm
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected,loud %t/te__st.cppm
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected -DNODIAGNOSTICS -Wno-reserved-module-identifier %t/te__st.cppm
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected,loud %t/std.cppm
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected -DNODIAGNOSTICS -Wno-reserved-module-identifier %t/std.cppm
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected,loud %t/std.foo.cppm
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected -DNODIAGNOSTICS -Wno-reserved-module-identifier %t/std.foo.cppm
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected,loud %t/std0.cppm
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected -DNODIAGNOSTICS -Wno-reserved-module-identifier %t/std0.cppm
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected,loud %t/std1000000.cppm
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected -DNODIAGNOSTICS -Wno-reserved-module-identifier %t/std1000000.cppm
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected,loud %t/should_diag._Test.cppm
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected -DNODIAGNOSTICS -Wno-reserved-module-identifier %t/should_diag._Test.cppm
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected,loud %t/system-module.cppm
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected -Wno-reserved-module-identifier %t/system-module.cppm
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected,loud %t/system._Test.import.cppm
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected -Wno-reserved-module-identifier %t/system._Test.import.cppm
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected,loud %t/user.cpp
+// RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify=expected -Wno-reserved-module-identifier %t/user.cpp
+
+//--- module.cpp
+module module;  // expected-error {{'module' is an invalid name for a module}}
+
+//--- import.cpp
+module import;  // expected-error {{'import' is an invalid name for a module}}
+
+//--- _Test.cpp
+module _Test;   // loud-warning {{'_Test' is a reserved name for a module}}  \
+                // expected-error {{module '_Test' not found}}
+
+//--- __test.cpp
+module __test; // loud-warning {{'__test' is a reserved name for a module}} \
+               // expected-error {{module '__test' not found}}
+
+//--- te__st.cpp
+module te__st; // loud-warning {{'te__st' is a reserved name for a module}} \
+               // expected-error {{module 'te__st' not found}}
+
+//--- std.cpp
+module std; // loud-warning {{'std' is a reserved name for a module}} \
+            // expected-error {{module 'std' not found}}
+
+//--- std.foo.cpp
+module std.foo; // loud-warning {{'std' is a reserved name for a module}} \
+                // expected-error {{module 'std.foo' not found}}
+
+//--- std0.cpp
+module std0; // loud-warning {{'std0' is a reserved name for a module}} \
+             // expected-error {{module 'std0' not found}}
+
+//--- std1000000.cpp
+module std1000000; // loud-warning {{'std1000000' is a reserved name for a module}} \
+                   // expected-error {{module 'std1000000' not found}}
+
+//--- module.cppm
+export module module; // expected-error {{'module' is an invalid name for a module}}
+
+//--- import.cppm
+export module import; // expected-error {{'import' is an invalid name for a module}}
+
+//--- _Test.cppm
+#ifdef NODIAGNOSTICS
+// expected-no-diagnostics
+#endif
+export module _Test;  // loud-warning {{'_Test' is a reserved name for a module}}
+
+//--- __test.cppm
+#ifdef NODIAGNOSTICS
+// expected-no-diagnostics
+#endif
+export module __test; // loud-warning {{'__test' is a reserved name for a module}}
+export int a = 43;
+
+//--- te__st.cppm
+#ifdef NODIAGNOSTICS
+// expected-no-diagnostics
+#endif
+export module te__st; // loud-warning {{'te__st' is a reserved name for a module}}
+export int a = 43;
+
+//--- std.cppm
+#ifdef NODIAGNOSTICS
+// expected-no-diagnostics
+#endif
+export module std;    // loud-warning {{'std' is a reserved name for a module}}
+
+export int a = 43;
+
+//--- std.foo.cppm
+#ifdef NODIAGNOSTICS
+// expected-no-diagnostics
+#endif
+export module std.foo;// loud-warning {{'std' is a reserved name for a module}}
+
+//--- std0.cppm
+#ifdef NODIAGNOSTICS
+// expected-no-diagnostics
+#endif
+export module std0;   // loud-warning {{'std0' is a reserved name for a module}}
+
+//--- std1000000.cppm
+#ifdef NODIAGNOSTICS
+// expected-no-diagnostics
+#endif
+export module std1000000; // loud-warning {{'std1000000' is a reserved name for a module}}
+
+//--- should_diag._Test.cppm
+#ifdef NODIAGNOSTICS
+// expected-no-diagnostics
+#endif
+export module should_diag._Test; // loud-warning {{'_Test' is a reserved name for a module}}
+
+//--- system-module.cppm
+// Show that being in a system header doesn't save you from diagnostics about
+// use of an invalid module-name identifier.
+# 34 "reserved-names-1.cpp" 1 3
+export module module;       // expected-error {{'module' is an invalid name for a module}}
+
+//--- system._Test.import.cppm
+# 34 "reserved-names-1.cpp" 1 3
+export module _Test.import; // expected-error {{'import' is an invalid name for a module}}
+
+//--- user.cpp
+// We can still use a reserved name on imoport.
+import std; // expected-error {{module 'std' not found}}
diff --git a/clang/test/Modules/reserved-names-2.cpp b/clang/test/Modules/reserved-names-2.cppm
similarity index 100%
rename from clang/test/Modules/reserved-names-2.cpp
rename to clang/test/Modules/reserved-names-2.cppm
diff --git a/clang/test/Modules/reserved-names-3.cpp b/clang/test/Modules/reserved-names-3.cppm
similarity index 100%
rename from clang/test/Modules/reserved-names-3.cpp
rename to clang/test/Modules/reserved-names-3.cppm
diff --git a/clang/test/Modules/reserved-names-4.cpp b/clang/test/Modules/reserved-names-4.cppm
similarity index 100%
rename from clang/test/Modules/reserved-names-4.cpp
rename to clang/test/Modules/reserved-names-4.cppm