diff --git a/stl/inc/complex b/stl/inc/complex
index 3a1958fdb1d..b5fb619f99e 100644
--- a/stl/inc/complex
+++ b/stl/inc/complex
@@ -21,7 +21,8 @@
 // https://learn.microsoft.com/cpp/build/arm64-windows-abi-conventions#base-requirements
 // Both floating-point and NEON support are presumed to be present in hardware.
 #define _FMP_USING_STD_FMA
-#elif defined(_M_IX86) || defined(_M_X64)
+#elif (defined(_M_IX86) || defined(_M_X64)) \
+    && !(defined(_BUILD_STD_MODULE) && defined(__clang__)) // TRANSITION, LLVM-195661
 #define _FMP_USING_X86_X64_INTRINSICS
 #include <__msvc_bit_utils.hpp>
 #include <intrin.h>
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 00b289b5c3c..683e0b6223d 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)
@@ -157,3 +168,6 @@ 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 63a9a94ee18..f91f1b40112 100644
--- a/tests/std/include/test_header_units_and_modules.hpp
+++ b/tests/std/include/test_header_units_and_modules.hpp
@@ -805,7 +805,9 @@ 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);
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..1cca3ff6358 100644
--- a/tests/std/tests/P2465R3_standard_library_modules/custom_format.py
+++ b/tests/std/tests/P2465R3_standard_library_modules/custom_format.py
@@ -22,7 +22,12 @@ def getBuildSteps(self, test, litConfig, shared):
         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]
+        if 'clang' in test.config.available_features:
+            inputPaths = ['-x', 'c++-module', *moduleUnits, '-x', 'none', *traditionalUnits]
+        else:
+            inputPaths = [*moduleUnits, *traditionalUnits]
 
         cmd = [test.cxx, *inputPaths, *test.flags, *test.compileFlags]
 
diff --git a/tests/std/tests/P2465R3_standard_library_modules/custombuild.pl b/tests/std/tests/P2465R3_standard_library_modules/custombuild.pl
index caece9c6b68..91a42c8e5cc 100644
--- a/tests/std/tests/P2465R3_standard_library_modules/custombuild.pl
+++ b/tests/std/tests/P2465R3_standard_library_modules/custombuild.pl
@@ -16,7 +16,14 @@ ()
     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, $stdCompatIxx);
+    my @traditionalUnits = ("test.cpp", "test2.cpp", "test3.cpp", "test4.cpp", "classic.cpp");
+    my @inputPaths;
+    if (($ENV{PM_COMPILER} // "") eq "clang-cl") {
+        @inputPaths = ("-x", "c++-module", @moduleUnits, "-x", "none", @traditionalUnits);
+    } else {
+        @inputPaths = (@moduleUnits, @traditionalUnits);
+    }
 
     Run::ExecuteCL(join(" ", @inputPaths, "/Fe$cwd.exe"));
 }
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..45f08071785 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
@@ -16,7 +16,10 @@ def getBuildSteps(self, test, litConfig, shared):
         userIxx = os.path.join(sourceDir, 'user.ixx')
 
         # Dependency order is important here:
-        inputPaths = [userIxx, testCpp]
+        if 'clang' in test.config.available_features:
+            inputPaths = ['-x', 'c++-module', userIxx, '-x', 'none', testCpp]
+        else:
+            inputPaths = [userIxx, testCpp]
 
         cmd = [test.cxx, *inputPaths, *test.flags, *test.compileFlags]
 
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..95adb3ba0ac 100644
--- a/tests/std/tests/VSO_1775715_user_defined_modules/custombuild.pl
+++ b/tests/std/tests/VSO_1775715_user_defined_modules/custombuild.pl
@@ -11,7 +11,12 @@ ()
     my $cwd = Run::GetCWDName();
 
     # Dependency order is important here:
-    my @inputPaths = ("user.ixx", "test.cpp");
+    my @inputPaths;
+    if (($ENV{PM_COMPILER} // "") eq "clang-cl") {
+        @inputPaths = ("-x", "c++-module", "user.ixx", "-x", "none", "test.cpp");
+    } else {
+        @inputPaths = ("user.ixx", "test.cpp");
+    }
 
     Run::ExecuteCL(join(" ", @inputPaths, "/Fe$cwd.exe"));
 }
diff --git a/tests/std/tests/modules_20_matrix.lst b/tests/std/tests/modules_20_matrix.lst
index 6ccb872fd81..7a2d5d5316a 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="-fmodule-output -fprebuilt-module-path=. -Wno-unqualified-std-cast-call /MD"
+PM_COMPILER="clang-cl" PM_CL="-fmodule-output -fprebuilt-module-path=. -Wno-unqualified-std-cast-call /MTd"
+PM_COMPILER="clang-cl" PM_CL="-fmodule-output -fprebuilt-module-path=. -Wno-unqualified-std-cast-call /MT"