diff --git a/libcxx/test/extensions/libcxx/depr/depr.c.headers/extern_c.pass.cpp b/libcxx/test/extensions/libcxx/depr/depr.c.headers/extern_c.pass.cpp
index 33b55c4bb195a..b7bdd841ea3e0 100644
--- a/libcxx/test/extensions/libcxx/depr/depr.c.headers/extern_c.pass.cpp
+++ b/libcxx/test/extensions/libcxx/depr/depr.c.headers/extern_c.pass.cpp
@@ -8,7 +8,7 @@
 
 // When building with modules, including headers inside extern "C" is an anti-pattern
 // that we don't want to support and can't support with LSV enabled.
-// UNSUPPORTED: clang-modules-build
+// ADDITIONAL_COMPILE_FLAGS: -fno-modules
 
 // Sometimes C++'s <foo.h> headers get included within extern "C" contexts. This
 // is ill-formed (no diagnostic required), per [using.headers]p3, but we permit
diff --git a/libcxx/test/extensions/libcxx/depr/depr.c.headers/include_as_c.sh.cpp b/libcxx/test/extensions/libcxx/depr/depr.c.headers/include_as_c.sh.cpp
index 635c7e3aa4f5f..dd9847f63253b 100644
--- a/libcxx/test/extensions/libcxx/depr/depr.c.headers/include_as_c.sh.cpp
+++ b/libcxx/test/extensions/libcxx/depr/depr.c.headers/include_as_c.sh.cpp
@@ -7,7 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 // We're building as C, so this test doesn't work when building with modules.
-// UNSUPPORTED: clang-modules-build
+// ADDITIONAL_COMPILE_FLAGS: -fno-modules
 
 // GCC complains about unrecognized arguments because we're compiling the
 // file as C, but we're passing C++ flags on the command-line.
diff --git a/libcxx/test/extensions/libcxx/depr/depr.c.headers/stdint_h.xopen_source.compile.pass.cpp b/libcxx/test/extensions/libcxx/depr/depr.c.headers/stdint_h.xopen_source.compile.pass.cpp
index 75a4ab908ce21..f665ec5a1b5db 100644
--- a/libcxx/test/extensions/libcxx/depr/depr.c.headers/stdint_h.xopen_source.compile.pass.cpp
+++ b/libcxx/test/extensions/libcxx/depr/depr.c.headers/stdint_h.xopen_source.compile.pass.cpp
@@ -7,7 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 // This test breaks when enabling LSV.
-// UNSUPPORTED: clang-modules-build
+// ADDITIONAL_COMPILE_FLAGS: -fno-modules
 
 // Test that limits macros are available when <stdint.h> is included
 // with or without macro _XOPEN_SOURCE=700.
diff --git a/libcxx/test/extensions/posix/xopen_source.gen.py b/libcxx/test/extensions/posix/xopen_source.gen.py
index ec0d981d67b2b..bea11e2c04ceb 100644
--- a/libcxx/test/extensions/posix/xopen_source.gen.py
+++ b/libcxx/test/extensions/posix/xopen_source.gen.py
@@ -15,7 +15,7 @@
 # Some parts of the code like <fstream> use non-standard functions in their implementation,
 # and these functions are not provided when _XOPEN_SOURCE is set to older values. This
 # breaks when building with modules even when we don't use the offending headers directly.
-# UNSUPPORTED: clang-modules-build
+# ADDITIONAL_COMPILE_FLAGS: -fno-modules
 
 # The AIX localization support uses some functions as part of their headers that require a
 # recent value of _XOPEN_SOURCE.
diff --git a/libcxx/test/libcxx-03/assertions/customize_verbose_abort.compile-time.pass.cpp b/libcxx/test/libcxx-03/assertions/customize_verbose_abort.compile-time.pass.cpp
index 69154c3f7eaff..bb44bc68eb1ce 100644
--- a/libcxx/test/libcxx-03/assertions/customize_verbose_abort.compile-time.pass.cpp
+++ b/libcxx/test/libcxx-03/assertions/customize_verbose_abort.compile-time.pass.cpp
@@ -7,7 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 // This compile-time customization requires cross-file macros, which doesn't work with modules.
-// UNSUPPORTED: clang-modules-build
+// ADDITIONAL_COMPILE_FLAGS: -fno-modules
 
 // Make sure that we can customize the verbose termination function at compile-time by
 // defining _LIBCPP_VERBOSE_ABORT ourselves. Note that this does not have any
diff --git a/libcxx/test/libcxx-03/assertions/modes/hardening_mode_incorrect_value.sh.cpp b/libcxx/test/libcxx-03/assertions/modes/hardening_mode_incorrect_value.sh.cpp
index 751ff7247445f..4f0abd8ab9d07 100644
--- a/libcxx/test/libcxx-03/assertions/modes/hardening_mode_incorrect_value.sh.cpp
+++ b/libcxx/test/libcxx-03/assertions/modes/hardening_mode_incorrect_value.sh.cpp
@@ -9,10 +9,11 @@
 // This test verifies that setting the hardening mode to a value that's not part of the predefined constants triggers
 // a compile-time error.
 
-// Modules build produces a different error ("Could not build module 'std'").
-// UNSUPPORTED: clang-modules-build
 // REQUIRES: verify-support
 
+// TODO: Investigate
+// ADDITIONAL_COMPILE_FLAGS: -fno-modules
+
 // Note that GCC doesn't support `-Wno-macro-redefined`.
 // RUN: %{verify} -U_LIBCPP_HARDENING_MODE -D_LIBCPP_HARDENING_MODE=42
 // Make sure that common cases of misuse produce readable errors. We deliberately disallow setting the hardening mode as
diff --git a/libcxx/test/libcxx-03/transitive_includes.gen.py b/libcxx/test/libcxx-03/transitive_includes.gen.py
index 6f99240436632..3ab9986bdb94c 100644
--- a/libcxx/test/libcxx-03/transitive_includes.gen.py
+++ b/libcxx/test/libcxx-03/transitive_includes.gen.py
@@ -77,7 +77,7 @@
 
 // When built with modules, this test doesn't work because --trace-includes doesn't
 // report the stack of includes correctly.
-// UNSUPPORTED: clang-modules-build
+// ADDITIONAL_COMPILE_FLAGS: -fno-modules
 
 // This test uses --trace-includes, which is not supported by GCC.
 // UNSUPPORTED: gcc
diff --git a/libcxx/test/libcxx-03/utilities/utility/pairs/pairs.pair/abi.non_trivial_copy_move.pass.cpp b/libcxx/test/libcxx-03/utilities/utility/pairs/pairs.pair/abi.non_trivial_copy_move.pass.cpp
index 1f5dae1232e37..65ae7de663162 100644
--- a/libcxx/test/libcxx-03/utilities/utility/pairs/pairs.pair/abi.non_trivial_copy_move.pass.cpp
+++ b/libcxx/test/libcxx-03/utilities/utility/pairs/pairs.pair/abi.non_trivial_copy_move.pass.cpp
@@ -8,7 +8,7 @@
 
 // The test suite needs to define the ABI macros on the command line when
 // modules are enabled.
-// UNSUPPORTED: clang-modules-build
+// ADDITIONAL_COMPILE_FLAGS: -fno-modules
 
 // <utility>
 
diff --git a/libcxx/test/libcxx/algorithms/alg.modifying.operations/copy_move_nontrivial.pass.cpp b/libcxx/test/libcxx/algorithms/alg.modifying.operations/copy_move_nontrivial.pass.cpp
index 162a3539d2308..f0da45d9bd281 100644
--- a/libcxx/test/libcxx/algorithms/alg.modifying.operations/copy_move_nontrivial.pass.cpp
+++ b/libcxx/test/libcxx/algorithms/alg.modifying.operations/copy_move_nontrivial.pass.cpp
@@ -7,11 +7,13 @@
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: c++03, c++11, c++14, c++17
-// In the modules build, adding another overload of `memmove` doesn't work.
-// UNSUPPORTED: clang-modules-build
+
 // GCC complains about "ambiguating" `__builtin_memmove`.
 // UNSUPPORTED: gcc
 
+// In the modules build, adding another overload of `memmove` doesn't work.
+// ADDITIONAL_COMPILE_FLAGS: -fno-modules
+
 // <algorithm>
 
 #include <cassert>
diff --git a/libcxx/test/libcxx/algorithms/alg.modifying.operations/copy_move_trivial.pass.cpp b/libcxx/test/libcxx/algorithms/alg.modifying.operations/copy_move_trivial.pass.cpp
index ff10c7919200d..e009438acb005 100644
--- a/libcxx/test/libcxx/algorithms/alg.modifying.operations/copy_move_trivial.pass.cpp
+++ b/libcxx/test/libcxx/algorithms/alg.modifying.operations/copy_move_trivial.pass.cpp
@@ -7,11 +7,13 @@
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: c++03, c++11, c++14, c++17
-// In the modules build, adding another overload of `memmove` doesn't work.
-// UNSUPPORTED: clang-modules-build
+
 // GCC complains about "ambiguating" `__builtin_memmove`.
 // UNSUPPORTED: gcc
 
+// In the modules build, adding another overload of `memmove` doesn't work.
+// ADDITIONAL_COMPILE_FLAGS: -fno-modules
+
 // <algorithm>
 
 // These tests check that `std::copy` and `std::move` (including their variations like `copy_n`) forward to
diff --git a/libcxx/test/libcxx/assertions/customize_verbose_abort.compile-time.pass.cpp b/libcxx/test/libcxx/assertions/customize_verbose_abort.compile-time.pass.cpp
index 69154c3f7eaff..bb44bc68eb1ce 100644
--- a/libcxx/test/libcxx/assertions/customize_verbose_abort.compile-time.pass.cpp
+++ b/libcxx/test/libcxx/assertions/customize_verbose_abort.compile-time.pass.cpp
@@ -7,7 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 // This compile-time customization requires cross-file macros, which doesn't work with modules.
-// UNSUPPORTED: clang-modules-build
+// ADDITIONAL_COMPILE_FLAGS: -fno-modules
 
 // Make sure that we can customize the verbose termination function at compile-time by
 // defining _LIBCPP_VERBOSE_ABORT ourselves. Note that this does not have any
diff --git a/libcxx/test/libcxx/assertions/modes/hardening_mode_incorrect_value.sh.cpp b/libcxx/test/libcxx/assertions/modes/hardening_mode_incorrect_value.sh.cpp
index 751ff7247445f..4f0abd8ab9d07 100644
--- a/libcxx/test/libcxx/assertions/modes/hardening_mode_incorrect_value.sh.cpp
+++ b/libcxx/test/libcxx/assertions/modes/hardening_mode_incorrect_value.sh.cpp
@@ -9,10 +9,11 @@
 // This test verifies that setting the hardening mode to a value that's not part of the predefined constants triggers
 // a compile-time error.
 
-// Modules build produces a different error ("Could not build module 'std'").
-// UNSUPPORTED: clang-modules-build
 // REQUIRES: verify-support
 
+// TODO: Investigate
+// ADDITIONAL_COMPILE_FLAGS: -fno-modules
+
 // Note that GCC doesn't support `-Wno-macro-redefined`.
 // RUN: %{verify} -U_LIBCPP_HARDENING_MODE -D_LIBCPP_HARDENING_MODE=42
 // Make sure that common cases of misuse produce readable errors. We deliberately disallow setting the hardening mode as
diff --git a/libcxx/test/libcxx/assertions/semantics/assertion_semantic_incorrect_value.sh.cpp b/libcxx/test/libcxx/assertions/semantics/assertion_semantic_incorrect_value.sh.cpp
index d7c1e26491ba9..67a0ed5aaa408 100644
--- a/libcxx/test/libcxx/assertions/semantics/assertion_semantic_incorrect_value.sh.cpp
+++ b/libcxx/test/libcxx/assertions/semantics/assertion_semantic_incorrect_value.sh.cpp
@@ -9,11 +9,12 @@
 // This test verifies that setting the assertion semantic to a value that's not part of the predefined constants
 // triggers a compile-time error.
 
-// Modules build produces a different error ("Could not build module 'std'").
-// UNSUPPORTED: clang-modules-build
 // UNSUPPORTED: c++03, libcpp-has-no-experimental-hardening-observe-semantic
 // REQUIRES: verify-support
 
+// TODO: Investigate
+// ADDITIONAL_COMPILE_FLAGS: -fno-modules
+
 // RUN: %{verify} -U_LIBCPP_ASSERTION_SEMANTIC -D_LIBCPP_ASSERTION_SEMANTIC=42
 // `hardening-dependent` cannot be set as the semantic (it's only an indicator to use hardening-related logic to pick
 // the final semantic).
diff --git a/libcxx/test/libcxx/depr/exception.unexpected/unexpected_disabled_cpp17.verify.cpp b/libcxx/test/libcxx/depr/exception.unexpected/unexpected_disabled_cpp17.verify.cpp
index b92f2baa02e47..10939ab91c69b 100644
--- a/libcxx/test/libcxx/depr/exception.unexpected/unexpected_disabled_cpp17.verify.cpp
+++ b/libcxx/test/libcxx/depr/exception.unexpected/unexpected_disabled_cpp17.verify.cpp
@@ -11,7 +11,7 @@
 // When built with modules, this test gives diagnostics like declaration of
 // 'unexpected' must be imported from module 'std.expected.unexpected' before
 // it is required. Therefore disable it in this configuration.
-// UNSUPPORTED: clang-modules-build
+// ADDITIONAL_COMPILE_FLAGS: -fno-modules
 
 // test unexpected
 
diff --git a/libcxx/test/libcxx/language.support/timespec_get.xopen.compile.pass.cpp b/libcxx/test/libcxx/language.support/timespec_get.xopen.compile.pass.cpp
index 134978d099ecf..7eafb77c2de9c 100644
--- a/libcxx/test/libcxx/language.support/timespec_get.xopen.compile.pass.cpp
+++ b/libcxx/test/libcxx/language.support/timespec_get.xopen.compile.pass.cpp
@@ -7,7 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 // This test breaks when enabling LSV.
-// UNSUPPORTED: clang-modules-build
+// ADDITIONAL_COMPILE_FLAGS: -fno-modules
 
 // UNSUPPORTED: c++03, c++11, c++14
 
diff --git a/libcxx/test/libcxx/transitive_includes.gen.py b/libcxx/test/libcxx/transitive_includes.gen.py
index 2b643e1f2ad48..8995482778d43 100644
--- a/libcxx/test/libcxx/transitive_includes.gen.py
+++ b/libcxx/test/libcxx/transitive_includes.gen.py
@@ -75,7 +75,7 @@
 
 // When built with modules, this test doesn't work because --trace-includes doesn't
 // report the stack of includes correctly.
-// UNSUPPORTED: clang-modules-build
+// ADDITIONAL_COMPILE_FLAGS: -fno-modules
 
 // This test uses --trace-includes, which is not supported by GCC.
 // UNSUPPORTED: gcc
diff --git a/libcxx/test/libcxx/utilities/utility/pairs/pairs.pair/abi.non_trivial_copy_move.pass.cpp b/libcxx/test/libcxx/utilities/utility/pairs/pairs.pair/abi.non_trivial_copy_move.pass.cpp
index 1f5dae1232e37..65ae7de663162 100644
--- a/libcxx/test/libcxx/utilities/utility/pairs/pairs.pair/abi.non_trivial_copy_move.pass.cpp
+++ b/libcxx/test/libcxx/utilities/utility/pairs/pairs.pair/abi.non_trivial_copy_move.pass.cpp
@@ -8,7 +8,7 @@
 
 // The test suite needs to define the ABI macros on the command line when
 // modules are enabled.
-// UNSUPPORTED: clang-modules-build
+// ADDITIONAL_COMPILE_FLAGS: -fno-modules
 
 // <utility>
 
diff --git a/libcxx/test/selftest/modules/std-and-std.compat-module.sh.cpp b/libcxx/test/selftest/modules/std-and-std.compat-module.sh.cpp
index 455674d6b9949..f61e8493c61cf 100644
--- a/libcxx/test/selftest/modules/std-and-std.compat-module.sh.cpp
+++ b/libcxx/test/selftest/modules/std-and-std.compat-module.sh.cpp
@@ -7,7 +7,6 @@
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
-// UNSUPPORTED: clang-modules-build
 // UNSUPPORTED: gcc
 
 // TODO: This test is currently written in a way that is specific to libc++, but it's really trying to test a property
@@ -20,6 +19,9 @@
 // The tests only look for the expected components and not the exact flags.
 // Otherwise changing the location of the module would break this test.
 
+// C++20 modules are incompatible with Clang modules
+// ADDITIONAL_COMPILE_FLAGS: -fno-modules
+
 // MODULE_DEPENDENCIES: std std.compat
 
 // RUN: echo "%{compile_flags}" | grep -- "-fmodule-file=std=.*/std.pcm .*/std.pcm"
diff --git a/libcxx/test/selftest/modules/std-module.sh.cpp b/libcxx/test/selftest/modules/std-module.sh.cpp
index e96c1e64b7275..ea9dbd5808937 100644
--- a/libcxx/test/selftest/modules/std-module.sh.cpp
+++ b/libcxx/test/selftest/modules/std-module.sh.cpp
@@ -7,7 +7,6 @@
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
-// UNSUPPORTED: clang-modules-build
 // UNSUPPORTED: gcc
 
 // TODO: This test is currently written in a way that is specific to libc++, but it's really trying to test a property
@@ -20,6 +19,9 @@
 // The tests only look for the expected components and not the exact flags.
 // Otherwise changing the location of the module would break this test.
 
+// C++20 modules are incompatible with Clang modules
+// ADDITIONAL_COMPILE_FLAGS: -fno-modules
+
 // MODULE_DEPENDENCIES: std
 
 // RUN: echo "%{compile_flags}" | grep -- "-fmodule-file=std=.*/std.pcm .*/std.pcm"
diff --git a/libcxx/test/selftest/modules/std.compat-module.sh.cpp b/libcxx/test/selftest/modules/std.compat-module.sh.cpp
index 4ec0ad8323d8d..8bce59b99279b 100644
--- a/libcxx/test/selftest/modules/std.compat-module.sh.cpp
+++ b/libcxx/test/selftest/modules/std.compat-module.sh.cpp
@@ -7,7 +7,6 @@
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
-// UNSUPPORTED: clang-modules-build
 // UNSUPPORTED: gcc
 
 // TODO: This test is currently written in a way that is specific to libc++, but it's really trying to test a property
@@ -16,6 +15,9 @@
 
 // XFAIL: has-no-cxx-module-support
 
+// C++20 modules are incompatible with Clang modules
+// ADDITIONAL_COMPILE_FLAGS: -fno-modules
+
 // Make sure that the compile flags contain the expected elements.
 // The tests only look for the expected components and not the exact flags.
 // Otherwise changing the location of the module would break this test.
diff --git a/libcxx/test/std/modules/std.compat.pass.cpp b/libcxx/test/std/modules/std.compat.pass.cpp
index e840f3c6b629c..0d1a4ac7d89c4 100644
--- a/libcxx/test/std/modules/std.compat.pass.cpp
+++ b/libcxx/test/std/modules/std.compat.pass.cpp
@@ -7,13 +7,15 @@
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: c++03, c++11, c++14, c++17
-// UNSUPPORTED: clang-modules-build
 // UNSUPPORTED: gcc
 
 // XFAIL: has-no-cxx-module-support
 
 // A minimal test to validate import works.
 
+// C++20 modules are incompatible with Clang modules
+// ADDITIONAL_COMPILE_FLAGS: -fno-modules
+
 // MODULE_DEPENDENCIES: std.compat
 
 import std.compat;
diff --git a/libcxx/test/std/modules/std.pass.cpp b/libcxx/test/std/modules/std.pass.cpp
index ca05825b3a186..4587dcb1b8178 100644
--- a/libcxx/test/std/modules/std.pass.cpp
+++ b/libcxx/test/std/modules/std.pass.cpp
@@ -7,13 +7,15 @@
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
-// UNSUPPORTED: clang-modules-build
 // UNSUPPORTED: gcc
 
 // XFAIL: has-no-cxx-module-support
 
 // A minimal test to validate import works.
 
+// C++20 modules are incompatible with Clang modules
+// ADDITIONAL_COMPILE_FLAGS: -fno-modules
+
 // MODULE_DEPENDENCIES: std
 
 import std;
diff --git a/libcxx/utils/libcxx/test/modules.py b/libcxx/utils/libcxx/test/modules.py
index bd4fbe78c1cdc..f70d976705d60 100644
--- a/libcxx/utils/libcxx/test/modules.py
+++ b/libcxx/utils/libcxx/test/modules.py
@@ -118,13 +118,15 @@ def write_lit_configuration(self):
         print(
             f"""\
 // UNSUPPORTED: c++03, c++11, c++14, c++17
-// UNSUPPORTED: clang-modules-build
 
 // REQUIRES: has-clang-tidy
 
 // The GCC compiler flags are not always compatible with clang-tidy.
 // UNSUPPORTED: gcc
 
+// C++20 modules are incompatible with Clang modules
+// ADDITIONAL_COMPILE_FLAGS: -fno-modules
+
 // MODULE_DEPENDENCIES: {self.module}
 
 // RUN: echo -n > {self.tmp_prefix}.all_partitions