diff --git a/stl/modules/std.compat.ixx b/stl/modules/std.compat.ixx
index a44c4149419..174004cf713 100644
--- a/stl/modules/std.compat.ixx
+++ b/stl/modules/std.compat.ixx
@@ -1,6 +1,14 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
+module;
+
+#ifdef __clang__
+#pragma clang diagnostic push
+// warning: 'std' is a reserved name for a module [-Wreserved-module-identifier]
+#pragma clang diagnostic ignored "-Wreserved-module-identifier"
+#endif // defined(__clang__)
+
 export module std.compat;
 
 export import std;
@@ -531,3 +539,7 @@ export using std::towlower;
 export using std::towupper;
 export using std::towctrans;
 export using std::wctrans;
+
+#ifdef __clang__
+#pragma clang diagnostic pop
+#endif // defined(__clang__)
diff --git a/stl/modules/std.ixx b/stl/modules/std.ixx
index d582fc80db7..b64780ad4f6 100644
--- a/stl/modules/std.ixx
+++ b/stl/modules/std.ixx
@@ -34,6 +34,17 @@ module;
 // <intrin.h> defines some types outside of `extern "C"` or `extern "C++"`.
 #include <intrin.h>
 
+#ifdef __clang__
+#include <malloc.h> // TRANSITION, LLVM-37969
+
+#pragma clang diagnostic push
+// warning: '#include <filename>' attaches the declarations to the named module 'std', which is not usually intended;
+//     consider moving that directive before the module declaration [-Winclude-angled-in-module-purview]
+// warning: 'std' is a reserved name for a module [-Wreserved-module-identifier]
+#pragma clang diagnostic ignored "-Winclude-angled-in-module-purview"
+#pragma clang diagnostic ignored "-Wreserved-module-identifier"
+#endif // defined(__clang__)
+
 export module std;
 
 #pragma warning(push)
@@ -155,3 +166,6 @@ export module std;
 #include <cwctype>
 
 #pragma warning(pop)
+#ifdef __clang__
+#pragma clang diagnostic pop
+#endif // defined(__clang__)
diff --git a/tests/std/include/test_header_units_and_modules.hpp b/tests/std/include/test_header_units_and_modules.hpp
index df85f9439e5..79d7275b5ea 100644
--- a/tests/std/include/test_header_units_and_modules.hpp
+++ b/tests/std/include/test_header_units_and_modules.hpp
@@ -284,6 +284,7 @@ void test_future() {
     assert(f.get() == 1729);
 }
 
+#if !(defined(__clang__) && defined(_M_ARM64EC)) // TRANSITION, LLVM-158341
 #if TEST_STANDARD >= 23
 void test_generator() {
     using namespace std;
@@ -297,6 +298,7 @@ void test_generator() {
     assert(ranges::equal(some_ints(bound), views::iota(0, bound)));
 }
 #endif // TEST_STANDARD >= 23
+#endif // ^^^ no workaround ^^^
 
 void test_initializer_list() {
     using namespace std;
@@ -755,7 +757,9 @@ constexpr bool impl_test_source_location() {
     using namespace std;
     const auto sl = source_location::current();
     assert(sl.line() == __LINE__ - 1);
+#ifndef __clang__
     assert(sl.column() == 38);
+#endif // !defined(__clang__)
 
 #ifdef __EDG__
     assert(sl.function_name() == "bool impl_test_source_location()"sv);
@@ -1198,9 +1202,11 @@ void all_cpp_header_tests() {
     test_fstream();
     test_functional();
     test_future();
+#if !(defined(__clang__) && defined(_M_ARM64EC)) // TRANSITION, LLVM-158341
 #if TEST_STANDARD >= 23
     test_generator();
 #endif // TEST_STANDARD >= 23
+#endif // ^^^ no workaround ^^^
     test_initializer_list();
     test_iomanip();
     test_ios();
diff --git a/tests/std/tests/P2465R3_standard_library_modules/custom_format.py b/tests/std/tests/P2465R3_standard_library_modules/custom_format.py
index d7d6a69fe11..f716d65e041 100644
--- a/tests/std/tests/P2465R3_standard_library_modules/custom_format.py
+++ b/tests/std/tests/P2465R3_standard_library_modules/custom_format.py
@@ -21,10 +21,21 @@ def getBuildSteps(self, test, litConfig, shared):
         test4Cpp = os.path.join(sourceDir, 'test4.cpp')
         classicCpp = os.path.join(sourceDir, 'classic.cpp')
 
-        # Dependency order is important here:
-        inputPaths = [stdIxx, stdCompatIxx, testCpp, test2Cpp, test3Cpp, test4Cpp, classicCpp]
+        moduleUnits = [stdIxx, stdCompatIxx]
+        traditionalUnits = [testCpp, test2Cpp, test3Cpp, test4Cpp, classicCpp]
 
-        cmd = [test.cxx, *inputPaths, *test.flags, *test.compileFlags]
+        if 'clang' in test.cxx:
+            for modulePath in moduleUnits:
+                cmd = [test.cxx, '-x', 'c++-module', modulePath, '--precompile', *test.flags, *test.compileFlags]
+                yield TestStep(cmd, shared.execDir, shared.env, False)
+
+            inputPaths = ['-x', 'c++-module', *moduleUnits, '-x', 'none', *traditionalUnits]
+            cmd = [test.cxx, *inputPaths, *test.flags, *test.compileFlags]
+        else:
+            # Dependency order is important here:
+            inputPaths = [*moduleUnits, *traditionalUnits]
+
+            cmd = [test.cxx, *inputPaths, *test.flags, *test.compileFlags]
 
         if TestType.COMPILE in test.testType:
             cmd += ['/c']
diff --git a/tests/std/tests/P2465R3_standard_library_modules/custombuild.pl b/tests/std/tests/P2465R3_standard_library_modules/custombuild.pl
index caece9c6b68..740d61b5221 100644
--- a/tests/std/tests/P2465R3_standard_library_modules/custombuild.pl
+++ b/tests/std/tests/P2465R3_standard_library_modules/custombuild.pl
@@ -15,9 +15,20 @@ ()
     my $stdIxx = "$stlModulesDir\\std.ixx";
     my $stdCompatIxx = "$stlModulesDir\\std.compat.ixx";
 
-    # Dependency order is important here:
-    my @inputPaths = ($stdIxx, $stdCompatIxx, "test.cpp", "test2.cpp", "test3.cpp", "test4.cpp", "classic.cpp");
+    my @moduleUnits = ($stdIxx, $stdCompatIxx);
+    my @traditionalUnits = ("test.cpp", "test2.cpp", "test3.cpp", "test4.cpp", "classic.cpp");
 
-    Run::ExecuteCL(join(" ", @inputPaths, "/Fe$cwd.exe"));
+    if ($ENV{PM_COMPILER} =~ m/clang/) {
+        for my $modulePath (@moduleUnits) {
+            Run::ExecuteCL("-x c++-module $modulePath --precompile");
+        }
+
+        Run::ExecuteCL(join(" ", "-x", "c++-module", @moduleUnits, "-x", "none", @traditionalUnits, "/Fe$cwd.exe"));
+    } else {
+        # Dependency order is important here:
+        my @inputPaths = ($stdIxx, $stdCompatIxx, "test.cpp", "test2.cpp", "test3.cpp", "test4.cpp", "classic.cpp");
+
+        Run::ExecuteCL(join(" ", @inputPaths, "/Fe$cwd.exe"));
+    }
 }
 1
diff --git a/tests/std/tests/VSO_1775715_user_defined_modules/custom_format.py b/tests/std/tests/VSO_1775715_user_defined_modules/custom_format.py
index 4432e6ba306..e4f45b0181d 100644
--- a/tests/std/tests/VSO_1775715_user_defined_modules/custom_format.py
+++ b/tests/std/tests/VSO_1775715_user_defined_modules/custom_format.py
@@ -15,10 +15,17 @@ def getBuildSteps(self, test, litConfig, shared):
         sourceDir = os.path.dirname(testCpp)
         userIxx = os.path.join(sourceDir, 'user.ixx')
 
-        # Dependency order is important here:
-        inputPaths = [userIxx, testCpp]
+        if 'clang' in test.cxx:
+            cmd = [test.cxx, '-x', 'c++-module', userIxx, '--precompile', *test.flags, *test.compileFlags]
+            yield TestStep(cmd, shared.execDir, shared.env, False)
 
-        cmd = [test.cxx, *inputPaths, *test.flags, *test.compileFlags]
+            inputPaths = ['-x', 'c++-module', userIxx, '-x', 'none', testCpp]
+            cmd = [test.cxx, *inputPaths, *test.flags, *test.compileFlags]
+        else:
+            # Dependency order is important here:
+            inputPaths = [userIxx, testCpp]
+
+            cmd = [test.cxx, *inputPaths, *test.flags, *test.compileFlags]
 
         if TestType.COMPILE in test.testType:
             cmd += ['/c']
diff --git a/tests/std/tests/VSO_1775715_user_defined_modules/custombuild.pl b/tests/std/tests/VSO_1775715_user_defined_modules/custombuild.pl
index cd5b08f5d5a..2461a3f7e7d 100644
--- a/tests/std/tests/VSO_1775715_user_defined_modules/custombuild.pl
+++ b/tests/std/tests/VSO_1775715_user_defined_modules/custombuild.pl
@@ -10,9 +10,14 @@ ()
 {
     my $cwd = Run::GetCWDName();
 
-    # Dependency order is important here:
-    my @inputPaths = ("user.ixx", "test.cpp");
+    if ($ENV{PM_COMPILER} =~ m/clang/) {
+        Run::ExecuteCL("-x c++-module user.ixx --precompile");
+        Run::ExecuteCL("-x c++-module user.ixx -x none test.cpp /Fe$cwd.exe");
+    } else {
+        # Dependency order is important here:
+        my @inputPaths = ("user.ixx", "test.cpp");
 
-    Run::ExecuteCL(join(" ", @inputPaths, "/Fe$cwd.exe"));
+        Run::ExecuteCL(join(" ", @inputPaths, "/Fe$cwd.exe"));
+    }
 }
 1
diff --git a/tests/std/tests/modules_20_matrix.lst b/tests/std/tests/modules_20_matrix.lst
index 6ccb872fd81..eb8a0f816e0 100644
--- a/tests/std/tests/modules_20_matrix.lst
+++ b/tests/std/tests/modules_20_matrix.lst
@@ -3,18 +3,25 @@
 
 RUNALL_INCLUDE ..\..\universal_prefix.lst
 RUNALL_CROSSLIST
-*	PM_CL="/w14365 /D_ENFORCE_FACET_SPECIALIZATIONS=1 /Zc:preprocessor"
+*	PM_CL="/w14365 /D_ENFORCE_FACET_SPECIALIZATIONS=1"
 RUNALL_CROSSLIST
 *	PM_CL="/w14640 /Zc:threadSafeInit- /EHsc /DTEST_STANDARD=20 /std:c++20"
 *	PM_CL="/w14640 /Zc:threadSafeInit- /EHsc /DTEST_STANDARD=23 /std:c++latest"
 RUNALL_CROSSLIST
-*	PM_CL="/MD"
-*	PM_CL="/MDd"
-*	PM_CL="/MT"
-*	PM_CL="/MTd"
-*	PM_CL="/MDd /analyze:only /analyze:autolog-"
-*	PM_CL="/MDd /GR- /D_HAS_STATIC_RTTI=0"
-*	PM_CL="/MDd /utf-8"
-RUNALL_CROSSLIST
-PM_CL=""
-ASAN	PM_CL="-fsanitize=address /Zi" PM_LINK="/debug"
+PM_CL="/MD /Zc:preprocessor"
+ASAN	PM_CL="/MD /Zc:preprocessor -fsanitize=address /Zi" PM_LINK="/debug"
+PM_CL="/MDd /Zc:preprocessor"
+ASAN	PM_CL="/MDd /Zc:preprocessor -fsanitize=address /Zi" PM_LINK="/debug"
+PM_CL="/MT /Zc:preprocessor"
+ASAN	PM_CL="/MT /Zc:preprocessor -fsanitize=address /Zi" PM_LINK="/debug"
+PM_CL="/MTd /Zc:preprocessor"
+ASAN	PM_CL="/MTd /Zc:preprocessor -fsanitize=address /Zi" PM_LINK="/debug"
+PM_CL="/MDd /analyze:only /analyze:autolog- /Zc:preprocessor"
+ASAN	PM_CL="/MDd /analyze:only /analyze:autolog- /Zc:preprocessor -fsanitize=address /Zi" PM_LINK="/debug"
+PM_CL="/MDd /GR- /D_HAS_STATIC_RTTI=0 /Zc:preprocessor"
+ASAN	PM_CL="/MDd /GR- /D_HAS_STATIC_RTTI=0 /Zc:preprocessor -fsanitize=address /Zi" PM_LINK="/debug"
+PM_CL="/MDd /utf-8 /Zc:preprocessor"
+ASAN	PM_CL="/MDd /utf-8 /Zc:preprocessor -fsanitize=address /Zi" PM_LINK="/debug"
+PM_COMPILER="clang-cl" PM_CL="-fprebuilt-module-path=. -Wno-unqualified-std-cast-call /MD"
+PM_COMPILER="clang-cl" PM_CL="-fprebuilt-module-path=. -Wno-unqualified-std-cast-call /MTd"
+PM_COMPILER="clang-cl" PM_CL="-fprebuilt-module-path=. -Wno-unqualified-std-cast-call /MT"